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Facultative river dolphins : conservation and social ecology of freshwater and coastal Irrawaddy dolphins in Indonesia
Kreb, D.
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Download date:04 Oct 2021 Facultativee River Dolphins m m
nservationn and Social Ecology of Freshwater andd Coastal Irrawaddy Dolphins in Indonesia
FACULTATIVE RIVER DOLPHINS:
CONSERVATION AND SOCIAL ECOLOGY OF FRESHWATER AND COASTAL IRRAWADDY DOLPHINS IN INDONESIA
ISBN: 90-76894-51-5 This research was carried out at the Institute for Biodiversity and Ecosystem Dynamics (IBED)/ Zoölogisch Museum Amsterdam (ZMA) Cover photo : Daniëlle Kreb Cover design : Jan van Arkel Printed by : Febodruk B.V., Enschede Financial support for printing received from: J.E. Jurriaanse Stichting and IBED Copyright © D. Kreb 2004
FACULTATIVE RIVER DOLPHINS:
CONSERVATION AND SOCIAL ECOLOGY OF FRESHWATER AND COASTAL IRRAWADDY DOLPHINS IN INDONESIA
ACADEMISCH PROEFSCHRIFT
Ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus prof. mr. P.F. van der Heijden ten overstaan van een door het college voor promoties ingestelde commissie, in het openbaar te verdedigen in de Aula der Universiteit op dinsdag 9 november 2004, te 14.00 uur
door
Daniëlle Kreb
geboren te Emmeloord, Noordoostpolder
Promotiecommissie:
Promotor: Prof. dr. F.R. Schram
Commissieleden: Prof. dr. S.B.J. Menken Prof. dr. W. Admiraal Prof. dr. P.H. van Tienderen Prof. dr. H.H.T. Prins Prof. dr. J.F. Borsani Dr. C. Smeenk
Faculteit: Natuurwetenschappen, Wiskunde en Informatica
Instituut: Instituut voor Biodiversiteit en Ecosysteem Dynamica
Untuk mas Budi dan Jannah
By Hari Moelyono TABLE OF CONTENTS
ACKNOWLEDGEMENTS……………………………………………………….i
SECTION I. GENERAL BACKGROUND
Chapter 1. A general introduction into the phenomenon of facultative river dolphins and the species Orcaella brevirostris………………………….1
Chapter 2. Observations on the occurrence of the Irrawaddy dolphin, Orcaella brevirostris, in the Mahakam River, East Kalimantan, Indonesia…….11 Zeitschrift für Säugetierkunde 64: 54-58, 1999
Chapter 3. Cetacean diversity and habitat preferences in tropical waters of East Kalimantan, Indonesia……………………………………….19 With Budiono, submitted manuscript
SECTION II. SURVEY TECHNIQUES FOR ABUNDANCE ESTIMATION
Chapter 4. Density and abundance of the Irrawady dolphin, Orcaella brevirostris, in the Mahakam River of East Kalimantan, Indonesia: A comparison of survey techniques………………………………..35 The Raffles Bulletin of Zoology, Supplement 10: 85-95, 2002
Chapter 5. Abundance of freshwater Irrawaddy dolphins in the Mahakam River in East Kalimantan, Indonesia, based on mark-recapture analysis of photo-identified individuals……………………………59 In press: Journal of Cetacean Research and Management, 2004
SECTION III. SOCIAL ECOLOGY AND CONSERVATION OF IRRAWADDY RIVER DOLPHINS
Chapter 6. Conservation management of small core areas: Key to survival of a critically endangered population of Irrawaddy River dolphins in Borneo………………………………………………………....81 With Budiono, in press: Oryx, 2004
Chapter 7. Living under an aquatic freeway: Effects of boats on Irrawaddy dolphins (Orcaella brevirostris) in a coastal and riverine environment in Indonesia….…………….……………………………………..105 With Karen D. Rahadi, in press: Aquatic Mammals, 2004
Chapter 8. Marked declines in populations of Irrawaddy dolphins…………...127 With Brian D. Smith and Isabel Beasley, Oryx 37: 401
Chapter 9. Social dynamics of facultative Irrawaddy River dolphins (Orcaella brevirostris) in Borneo: Impacts of habitat…………………………133 Submitted manuscript
Chapter 10. Impacts of habitat on the acoustics of coastal and freshwater Irrawaddy dolphins, Orcaella brevirostris in East Kalimantan, Indonesia…………………………………….…………………...161 With Junio F. Borsani
SECTION IV. GENERAL DISCUSSION- POPULATIONS AND LONG-TERM PROGNOSIS FOR SURVIVAL
Chapter 11. Freshwater distribution of Irrawaddy dolphins based on river “vagrancy” or allopatric “speciation”?……………………………185
Chapter 12. Predicting long-term survival of riverine Irrawaddy dolphins (Orcaella brevirostris) in East Kalimantan using Population Viability Analysis ………………………………………………...199
APPENDIX I Irrawaddy dolphins in the Mahakam River, Indonesia…………213
APPENDIX II Monitor and evaluate ongoing threats to the Irrawaddy Dolphins in the Mahakam River of Indonesia…………………215 Appendix 1, pp. 88-89; Appendix 2, p. 56 in: R.R. Reeves, B.D. Smith, E.A. Crespo and G.N. di Sciara (eds.) (2003). 2002-2010 Conservation Action Plan for the World’s Cetaecans. Dolphins, whales and porpoises. IUCN, Gland, Switzerland
SUMMARY Facultative river dolphins: Conservation and social ecology of freshwater and coastal populations of Irrawaddy dolphins in Indonesia …….………………………………………………….217
SAMENVATTING Facultatieve rivierdolfijnen: Bescherming en sociale ecologie van zoet- en zoutwater populaties van Irrawaddy dolfijnen, Orcaella brevirostris in Oost Kalimantan, Indonesië………….221
RINGKASAN Lumba-lumba sungai: Konservasi dan sosial ekologi dari populasi lumba-lumba Irrawaddy, Orcaella brevirostris pada air tawar dan laut di Kalimantan Timur, Indonesia………………………………….225
CURRICULUM VITAE………………………………………………………...229 Preface and acknowledgements
PREFACE AND ACKNOWLEDGEMENTS
This research began with a simple telephone call from Indonesia to Scotland, where at that time I was assisting a radio-tracking study on wildcats, by my good friend and colleague Vincent Nijman who asked me if I knew that there were river dolphins in the Mahakam River in East Kalimantan (for which tip I owe him). Since I so far had only heard about the obligate river dolphins in the Amazon, Ganges, Indus and Yangtze Rivers, which had already captured my interest and imagination, I was surprised and interested to find out more about it. From the sides of the Provincial Wildlife Conservation Department of East Kalimantan (BKSDA Kaltim) and WWF Indonesia (thanks to former staff member Ron Lilley), there was an interest to conduct a preliminary survey in the freshwater dolphins in the Mahakam, which were locally referred to as the pesut. Thanks to the help of Dr Peter J.H. van Bree, Curator Emeritus of the Zoological Museum of Amsterdam, who helped me prepare a proposal to join the survey and find a sponsor through Marc Argeloo and Jikkie Jonkman from WNF Nederland, I soon flew off on my way to meet my first river dolphin in real. I should say that my first observation of the dolphins thrilled me with admiration and I felt that this survey was not to be my last one especially after the numbers we encountered during the survey were rather low and visible threats were numerous. The research really had to be started from the scratch as no previous systematic studies on Irrawaddy dolphins in East Kalimantan had been done upon which to build. The difficulties in studying cetaceans in general is that it requires a great deal of organisation and preparation in order to work as efficiently as possible because of the use of boats, which sometimes is an unpredictable and costly factor. Some creativity and patience was required at times when the working schedule needed to be adjusted when dealing with engine problems or during bad weather conditions, especially at sea where lack of freshwater also was problematic at times. During this research I have not only learned a lot about dolphins, boats, rivers and seas, but also about local human cultures, of which I found the mutual respect and hospitality that I encountered heart warming. My impressions, which turned out to be realistic based on interviews, were that many fishermen in the Mahakam actually had an appreciation for the dolphins and did not wish the dolphins to disappear from the river This encouraged me in my attempts to set up a conservation program. A range of activities focusing on increasing local awareness of the younger generation, fishermen, politics
i Preface and acknowledements
and society in general, have been conducted since late 2000 until now by the local NGO Yayasan Konservasi RASI (Conservation Foundation for Rare Aquatic Species of Indonesia). I am most grateful to my promoter Professor Frederick R. Schram for taking this project on his shoulders and for his enduring support and scientific guidance. All my manuscripts have been commented and corrected by him. In this regard, a special note of thanks should go to Dr. Arne Mooers, who brought Fred and me together. I also owe a great deal of gratitude to Dr Peter J.H. van Bree, who helped me throughout the study with literature, good advice, and assistance with locating other support. I also thank Dr Jan Wattel for his help in finding financial support. Harm van der Geest is also thanked for his good tip. My special thanks go to my first counterpart Ir Ade M. Rachmat (M.Sc.), former head of the BKSDA Kaltim, who has so unfortunately deceased some months ago. He invited me as a guest to participate in the first preliminary survey, covered all costs and had me stay in his house in Samarinda in between the surveys. My next counterparts Ir Padmo Wiyoso, former head of BKSDA Kaltim and Prof A. Arrifien Bratawinata of the University of Mulawarman in Samarinda (UNMUL) are also thanked for their support of the study. I would like to thank the Indonesian Institute for Sciences (LIPI), the Provincial Wildlife Conservation Department (BKSDA Kaltim) and local governments of Central- (KUKER) and West Kutai (KUBAR) for granting permission to conduct field research. At the Division of Inter-Institutional Cooperation of LIPI, Ibu Ina Syarief and Ibu Krisbiwatti have been very helpful in arranging necessary permits and letters and are thanked for this. I thank all my field assistants gratefully: Hardy, Syafrudin, Chaironi, Zainudin, Syoim, Rudiansyah, Bambang, Sonaji, Marzuki, Iwiet, Munadianto, Hendra, Deni, Ramon, Audrie and particularly Ahank, Arman, Budiono, Yusri, Karen and Syachrani, who assisted during most surveys and with full dedication. The boatsmen Pak Sairapi, Pak Muis, Pak Mahyuni, Pak Iwan, Pak Johan, Pak Kasino and Pak Anto are thanked gratefully. I also enjoyed the company of Djupri, Fleur Butcher and Pak Sega during the first preliminary survey in 1997. Funding for fieldwork was provided by Ocean Park Conservation Foundation, Hong Kong; Martina de Beukelaar Stichting; Stichting J.C. van der Hucht Fonds; Gibbon Foundation; Netherlands Ministry of Agriculture, Nature Management and Fisheries (PIN/ KNIP); Van Tienhoven Stichting; World Wildlife Fund for Nature (Netherlands); Stichting Doctor Catharina van Tussenbroek Fonds, Coastal Resource
ii Preface and acknowledgements
Management Program/ Proyek Pesisir and Amsterdamse Universiteits Vereniging. Funds for printing costs were provided by the Jurriaanse Stichting and the Institute for Biodiversity and Ecosystem Dynamics. All sponsors mentioned are acknowledged gratefully. During workshops and congresses it has been very pleasant to meet with a number of cetacean colleagues of which some have been particularly helpful during the research; First of all I owe a great deal of gratitude to Thomas A. Jefferson, who allowed me to assist in his research on Indo-Pacific humpback dolphins in Hong Kong for 2 months in 1998; he taught me many useful survey techniques and has always been helpful in all my research questions and requests for literature. I also thank the “Ocean Park crew” for their support, interest in my project and their good company. Randall Reeves, William Perrin, Bernd Würsig, Brian Smith, Fabrizio Borsani, Tony Martin, Jeanette Thomas, Tamara Mcguire, Ian Baird, Randall Wells, Vincent Nijman, Miquel Vences, Isabel Beasley, Guido Parra, Chris Smeenk, Martjan Lammertink, Gabriella Fredriksson, Willie Smits, Arne Mooers, Kees Hazevoet, Martin Genner, Resit Sözer, Matthijs Couwelaar, Bert Hoeksema and Annelies Pierrot-Bults are thanked for sending me literature, exchanging ideas, reviewing my manuscripts, and their general support. I also thank my colleagues at the Zoological Museum, in particular Tineke Prins, Martjan Lammertink, Vincent Nijman, Mansour Aliabadi, Miquel Vences, Kees Roselaar, Tonnie Dunselman, Andre Walgreen, Adri Rol, Mohamed El Moussaoui, Wouter Kraandijk, Thomas van Wissen, Hans van Brandwijk, Tatjana Das, Wouter Los and colleagues at ETI for providing a pleasant working environment and support. I am grateful to all librarians of the Plantage Library and the Zoological Museum for use of their facilities. I owe a great deal to Fabrizio Borsani for providing me with a good hydrophone to make acoustic recordings. Kelly Robertson is thanked for analysing genetic skin samples of the pesut (this study is still in progress). All the co-authors in manuscripts of this thesis are thanked for their cooperation. I would like to thank my husband Budiono and Gustinah for translation of the summary and all chapter abstracts in Bahasa Indonesian. Tineke Prins and Kees Hazevoet are acknowledged for correcting the Dutch summary and Jan van Arkel for preparing the cover design and some figures for this thesis. I also thank Hari Moelyono for his nice pen-drawings of the pesut and for handling the main editing process of the small Video CD on the pesut and its conservation. I thank Syachrani and Erwin van Faassen for solving all my computer problems and program installations.
iii Preface and acknowledements
Paulien de Bruijn is thanked for providing a Dutch breeze for a while during my long stay in Indonesia. I also thank her and Linda Zwiggelaar for their help as paranymphs. My daughter was born when I was still in the middle of my analysis and thanks to Gaguk and the Titaantjes, especially Martine, Melanie, and Alette, who took over a great deal of her daily care, I was able to continue my analysis both in Indonesia and in the Netherlands. I am also especially grateful for the participation of Prof. dr. W. Admiraal, Prof. dr. P.H. van Tienderen, Prof. dr. S.B.J. Menken, Prof. dr. H.H.T. Prins, Prof. dr. J.F. Borsani, and Dr. C. Smeenk in the Doctorate Commission. I would like to express my gratitude to all fishermen and residents mostly along the Mahakam River, Balikpapan Bay and Berau Islands who participated in interviews or provided us with information on the pesut and/ or cetacean species or on fisheries. I am also grateful for the hospitality with which our team was always received in every village to which we came. I thank my foster family of Pak Usman in Long Bagun, the family of Pak Mahyuni in Data Bilang, the family of nenek and Masman, the family of Nina losmen in Muara Pahu, and the family of Pak Yan in Muara Kaman for their true friendship. Naturally, I would like to thank my best friends and family, especially Joleen, Linda, and my sisters Conny and Monique in the Netherlands and family in Indonesia, who have been very encouraging to me to pursue my scientific research, but in whose company I could also relax and have fun and enjoy the other non-scientific side of life. I thank Ronald for his encouragements and for sharing mountain walks through which I developed determination and which set off my exploration of fauna and flora. I am very grateful to my parents, who have always helped me with everything I needed so that I could concentrate on my work and have no other worries. Finally, I would like to thank my daughter Jannah and my husband mas Budi, for being the lights of my life, and for giving me the necessary distraction and faith in my work - Damai Selamanya.
iv General introduction in facultative river dolphins and Orcaella brevirostris
CHAPTER 1
A general introduction into the phenomenon of facultative river dolphins and the species Orcaella brevirostris
Behaviours displayed by coastal Irrawaddy dolphins in captivity ( Laem Sing, Thailand) such as this spy-hopping behaviour, has also been observed in wild Irrawaddy dolphins in the Mahakam River.
1 Chapter 1
(Facultative) river dolphins and river wanderers
The order of Cetacea is composed of a variety of 85 recognized species and 41 subspecies of baleen whales and toothed whales and dolphins (Perrin et al., 2002; Reeves et al., 2003). Cetaceans have originally successfully spread out over vast areas of the worlds’ oceans and inner seas. The freshwater habitat has been “conquered” at first by four “older” river dolphin (sub)species, the Amazon dolphin or boto Inia geoffrensis, the Yangtze dolphin or baiji Lipotes vexilifer, the Ganges dolphin or shushuk Platanista gangetica gangetica and the Indus dolphin or bhulan P. gangetica minor where they adapted even further to “microhabitats”; lakes, confluence areas, rapid stream areas (Best & da Silva, 1993) and flooded forests (Layne, 1958). The boto has been suggested to have entered the Amazon basin from the Pacific some 15 million years ago (Grabert, 1983) or more recently (1.8-5 million years ago) from the Atlantic Ocean (Brooks, et al.; Gaskin, 1982). Occasional river wanderers include representatives of several families of toothed whales: Within the Delphinidae family, the Indo-Pacific humpbacked dolphin Sousa chinensis has been recorded in the Fuchow River (now: Fuchung Jiang) and rivers flowing to Canton (Guangzhou) and 750 miles up the Yangtze, at least as far as Hankow (now: Hankou, near Wuhan) (True, 1889). In Indonesia, they are reported to occur about 30 km upstream the Kapuas River in western Kalimantan (information of local fishermen) and in the Dali River in north-eastern Sumatra (Suwelo, 1988). In Australia, they are found in the Brisbane River in Queensland (Klinowska, 1991). The Atlantic hump-backed dolphin Sousa teuszii is known to enter the Niger River and the Baniala River in Nigeria (Klinowska, 1991).This species is also known to occur in the Rio Gêba in Guiné Bissau (Spaans, 1990). The common dolphin Delphinus delphis has been observed in the Hudson River, north-eastern USA, as far as 230 km (Stoner, 1938). Bottlenose dolphins Tursiops truncatus have been reported in the Casamance River in Senegal and in the Rio Gêba in Guinea-Bissau (Spaans, 1990). They are expected to occur on other rivers in western Africa as well (Hazevoet, pers. comm. 1997). Two representatives of the Cephalorhynchinae, the Chilean or black dolphin Cephalorhynchus eutropia and the New-Zealand dolphin Cephalorhynchus hectori, occur in rivers. The first one moves at least 5 km up the Valdavia River (Goodall et al., 1988). The latter often enters and travels some distance upstream in several turbid rivers in flood during their northwards summer ‘migrations’ (Watson 1981). Within the family of Phocoenidae, the harbour porpoise Phocoena phocoena, can also be found in tidal rivers (Klinowska, 1991). One individual was described to have reached Paris after entering the Seine River and in the 17th century harbour porpoises could be found in the canals of Amsterdam (Delsman, 1922; van Bree, pers. comm. 1997). Even two species of baleen whales might occasionally wander upstream rivers. The minke whale Balaenoptera acutorostrata and the humpback whale Megaptera novaeangliae, have been recorded respectively 16 km upstream the Snohomish River in Washington State (Scheffer & Slipp, 1948) and 16 km up the Sacramento River in northern California (Warhol, 1986).
2 General introduction in facultative river dolphins and Orcaella brevirostris
Although the cetaceans above may move very far upstream and even remain there for weeks, they are most likely temporary visitors. Their usual range includes river mouths, bays, lagoons, estuarine complexes and virtually any shallow water marine region. However, the most conspicuous river ‘wanderer’ is the white whale or beluga Delphinapterus leucas. This large, white dolphin moves regularly and sometimes in groups, very far upstream rivers. Below follows a list of those rivers where Belugas have been recorded very far upstream, or where they have been reported more often. In Alaska, one individual was found at 1500 km from the Bering Sea upstream the Yukon river near the Kuskokwim River and Nulato (Nelson & True, 1887). According to Lee (1878) the Beluga occurs, during the summer months, in all the mouths and in nearly all bigger rivers at the west coast of the Hudson bay as well as the Greenland coast. The St. Lawrence Beluga population in Quebec is regularly found at Ile de Coudres, about 600 km upstream the mouth. In almost all big river mouths and rivers in Russian-Siberian waters, groups of Belugas were regularly seen some hundred up to two thousand km upstream. Kleinenberg et al. (1969) provided an overview of their Russian-Siberian distribution. The most extreme wanderings included a record of 2000 km upstream the Amur River in eastern Siberia until the Argun River in China . In Europe, their river wanderings are very occasional and therefore caused much excitement and publicity. The occurrence of a Beluga in the Schelde River in Belgium until Dendermonde (c. 100 km from the mouth) in 1711 caused so much excitement that a statue of 2.5 meter length was made and is carried like a trophy around the town at each 25th anniversary. (Gewalt, 1976). The one- month wandering of a Beluga in 1966 up the river Rhein until Bad Honnef (c. 400 km from the mouth) made world wide news in press (Gewalt, 1976). Underlying factors of these riverine migrations are explained in terms of the riverine migration of prey species. For example, salmons are one of their prey species, which move upstream to lay their eggs and they become an easier prey in the shallow waters where they cannot swim so fast. Other reasons were proposed by Mohr (1952 in Gewalt, 1976) in terms of dolphins having lost their direction and in terms of their active curiosity to explore. The fact that they also occur as groups in the river and that this happens frequently might also indicate that their riverine occurrence is probably based on more than an error. Three species of cetaceans, which have established separate populations in rivers and in near-shore, marine waters include the species Irrawaddy dolphin Orcaella brevirostris, the tucuxi Sotalia fluviatilis and the finless porpoise Neophocaena phocaena (Smith & Jefferson, 2002). These represent more recent colonizers of freshwater habitats, in comparison to the obligate river dolphins, and they have been described as “facultative” river cetaceans, due to their species’ flexibility to inhabit marine and freshwater environments (Leatherwood & Reeves, 1994). Nevertheless, the freshwater populations may actually represent obligate freshwater populations. The time period of invasion or process of adaptation of these relative newcomers in rivers are unknown and some hypothesis are offered in Chapter 11. The tucuxi is sympatrically ocurring throughout much of its range with the boto and inhabits rivers and lake
3 Chapter 1 systems of Amazonia, the lower Orinoco River, and coastal marine waters from the Florianópolis region of Brazil, north to at least Nicaragua (Carr & Bonde, 2000; IWC, 2001). The finless porpoise occurs sympatrically with the baiji in the Yangtze River and lakes system. Additionally, they inhabit shallow nearshore marine waters along the coasts of southern and eastern Asia, from the Persian Gulf east to Sendai Bay, Japan, and south to Java (Reeves et al., 1997, 2000; Parsons & Wang, 1998; Kasuya, 1999). Just like the finless porpoise, Irrawaddy dolphins have a wide, but patchily distribution occurring in shallow, near-shore tropical and subtropical marine waters of the Indo- Pacific, from north-eastern India in the west, northeast to the Philippines and south to northern Australia, including most of the Indonesian archipel (Dolar et al., 2002; Rudolph et al., 1997; Stacey & Leatherwood, 1997; Stacey & Arnold, 1999). Their coastal distribution is mostly concentrated in estuaries and mangrove bay areas (Chapter 3). Their freshwater distribution is limited to three major river systems: the Mahakam in Indonesia, the Ayeyarwady in Myanmar, and the Mekong in Laos, Cambodia and Vietnam. Besides, they also occur in two completely or partially isolated brackish water bodies, including Chilka Lake in India and Songkhla Lake in Thailand (Beasley et al., 2002; Smith & Jefferson, 2002). Although the concept of stocks was already commonly applied in conservation and management of whales by the International Whaling Commission, in the 1988- 1992 Action Plan of the IUCN/SSC Cetacean Specialist Group a rationale was provided by Perrin (1988), for also including endangered populations besides species in conservation action plans. In the next action plan of the IUCN/SSC Cetacean Specialist Group (Reeves & Leatherwood, 1994) two projects were proposed involving the investigation of the riverine status of facultative river dolphins, namely: “Investigation of status and conservation of Irrawaddy dolphins in southern Asia” and “Investigation of status and establishing protected areas for pesut in Indonesia”. Following the latter recommendation a preliminary survey was initiated in 1997 to assess threats, distribution range and densities of the Irrawaddy dolphin in the Mahakam, locally referred to as pesut (Chapter 2), after which a more intensive research was carried out in the form of this Ph.D study. Whether cetacean species are estuarine and/ or occasional river visitors, or are obligate riverine, it is clear that many species depend on the river or the river run-off in estuaries and are very vulnerable to the effects of habitat degradation. Therefore, a holistic approach of protection of the entire riverine ecosystem is of utmost importance within the conservation of (facultative) river dolphins. However, the key will lie in effective conservation of manageable sites, in which positive results for the local community may serve as exemplary for other sites so that gradually a large proportion of the river may be effectively protected (Chapter 6).
Orcaella brevirostris (Gray, 1866)
Type species: Orca (Orcaella) brevirostris Gray, 1866: 285. Type locality:
4 General introduction in facultative river dolphins and Orcaella brevirostris
“East coast of India in the harbour of Vizagapatam (presently named Vishakhapatnam)”. Orcaella fluminalis Anderson, 1871:80. Type locality: “1500 km from the mouth in the fomerly named Irrawaddy River in Burmah (presently named Ayeyarwady River, Myanmar)”. General concensus: One species, Orcaella brevirostris (Loze, 1973; Pilleri & Gihr, 1974; Rice, 1998). Common name: Irrawaddy dolphin; local name in the Mahakam River: pesut.
The most recent systematic placement of the species is within the Order of Cetacea, Suborder Odontoceti, Superfamily Delphinoidea, Family Delphinidae, Subfamily Orcininae. Although, Orcaella has been placed in other families, i.e., Delphinapteridae together with the beluga Delphinapterus leucas (Kasuya, 1973); Monodontidae together with the beluga and narwhal Monodon monoceros (Barnes, 1984; Gaskin, 1982; Pilleri et al., 1989); Orcaellidae (Nishiwaki, 1973), the most recent morphological and molecular data suggest that Irrawaddy dolphins belong to the family of Delphinidae (Arnold & Heinsohn, 1996; Le Duc et al., 1999). They have been placed in the following subfamilies based on morphological data: Orcininae (Fraser & Purves, 1960); Globicephalinae (de Muizon, 1988); the monotypic Orcaellinae (Perrin, 1989). Most recent research involved the use of molecular data, which placed the Irrawaddy dolphin closest to the killer whale Orcinus orca (Arnason & Gullberg, 1996) and into the Orcininae (LeDuc et al., 2002), although the relationship was relatively distant and bootstrap support was low. The taxonomic status at the intraspecific level remains unclear (Stacey & Arnold, 1999). However, recent studies of skull morphology suggest possible specific differences between Australia/ New Guinea and Southasian forms (Beasley et al., 2002) Earlier a short account of the marine and freshwater distribution of Irrawaddy dolphins was given. Figure 1 shows locations of actual records, which are mostly based on Mörzer Bruyns, 1966, Stacey & Leatherwood, 1998, and some derived from various other sources. In Indonesian waters they were found some 16 km upstream the Belawan Deli River (north-eastern Sumatra); Surabaya (northeast coast Java); Cilacap, Segara Anakan (south coast of Central Java); Makassar (southwest coast Sulawesi); between Pulo Superiori and Pulo Biak; mouths of muddy waters (south coast West Papua), Mahakam River, Belitung Island (Mörzer Bruyns, 1966); coastal area of Kumai River (Central Kalimantan) (Kartasana & Suwelo, 1994); Seribu Islands (Java Sea); delta Kendawangan River(south coast West Kalimantan) (Rudolph et al., 1997), c. 380 km upstream the Barito River below Puruk Cahu (South Kalimantan); Kajan River (north East Kalimantan) (Delsman, 1922); Balikpapan and Sangkulirang Bay and coastal areas in between (coast East Kalimantan); Mahakam Delta (Kreb, this thesis, chapter 3); confluence of Sekonjer River and Kumai River (Central Kalimantan); delta Sesayap River (north East Kalimantan) (Erik Meijaard, in litt., 1997).
5
Asia. Black dots representing actual records from 6 literature and own observations. Map with Irrawaddy dolphin distribution in South East Figure 1. Chapter 1
General introduction in facultative river dolphins and Orcaella brevirostris
Aims of the study
The general aims of this study were to investigate the conservation biology, social organization, social communication, and marine and freshwater distribution patterns (stock identification) of the freshwater and coastal Irrawaddy dolphin populations in south East Asia with special reference to the Mahakam River in East Kalimantan and adjacent coastal areas. The study’s ultimate goal is to contribute to the conservation of Indonesia’s only freshwater dolphin population that inhabits the Mahakam River and lakes in East Kalimantan, Indonesia, to fill in the gap in literature on social systems within (facultative) river dolphins and to an appropriate action plan to ensure the survival of the pesut. Detailed objectives involved: Conducting a preliminary survey prior to the Ph.D study to assess total dolphin distribution range and dolphin densities in different river areas, as well as to obtain an indication of threats to the population (Chapter 2); to assess cetacean diversity and distribution of coastal Irrawaddy dolphins along the coast of East Kalimantan (Chapter 3); to assess total population abundance through different seasons and by aid of several survey techniques, i.e., direct counts, density sampling, and mark-recapture analysis through photo-identification (Chapters 4, 5); to study habitat use and preferences, site fidelity, short-and long-term movement patterns, threat analysis and developing a conservation program to protect the pesut population and its habitat in the Mahakam River (Chapter 6); to study specifically the effects of boats on dolphins’ (surfacing) behaviour (Chapter 7); to provide an overview of status and threats of Irrawaddy dolphins throughout South East Asia (Chapter 8); to compare the social structures and breeding strategies of coastal and freshwater populations of Irrawaddy dolphins and additionally, study association patterns of individual dolphins in the Mahakam (Chapter 9); to compare vocalizations of coastal and freshwater populations of Irrawaddy dolphins and among different sites within the river; to investigate whether whistle shapes and frequencies are more determined by ecological, genetic or social factors; and to compare the vocalizations of all populations in East Kalimantan with those from Irrawaddy dolphins in Australian coastal waters and in the Mekong River to investigate whether the acoustics of the Irrawaddy dolphin follow an ecological (freshwater/ coastal) and/or geographical separation (Asia/ Indonesia/ Australia) (Chapter 10); to study the process of isolation of distinctive river and coastal Irrawaddy dolphins through their distribution patterns, (social) biology, historical biogeography, comparisons with other facultative riverine dolphin species. Although genetic material of both riverine and coastal populations were collected, unfortunately, only the skin cell material of the riverine populations yielded enough DNA to be used in the genetic analysis (Chapter 11); finally, to conduct a population viability analysis for a long-term prognosis of survival of the pesut population and assess the direction where conservation effort is mostly required and which events determine the viability of the population (Chapter 12).
7 Chapter 1
References
Anderson, J. 1871. Description of a new cetacean from the Irrawaddy River, Burma Orcaella fluminalis Anderson. Proceedings of the Zoological Society of London 39: 142-144. Carr, T. & Bonde, R.K. 2000. Tucuxi (Sotalia fluviatilis) occurs in Nicaragua, 800 km north of its previously known range. Marine Mammal Science 16: 447-452. Gewalt, W. 2001. Der Weisswal: Delphinapterus leucas. Die Neue Brehm-Bücherei, Hohenwarsleben, Westarp-Wiss. [In German]. Goodall, R.N.P., Norris, K.S., Galeazzi, A.R., Oporto, J.A. & Cameron, I.S. (1988). On the Chilean dolphin, Cephalorhynchus eutropia (Gray, 1846). Rep. Int. Whal. Commn, Spec. Issue 9: 197-257. Gray, J. E. 1866. Catalogue of the seals and whales in the British Museum, 2nd edition. British Museum, London, 402 pp. IWC. 2001a. Report of the standing sub-committee on small cetaceans. Journal of Cetacean Research and Management (Special Issue) 2: 1-60. Kartasana, G.F. & Suwelo, I.S. 1994- . The existence of Irrawaddy dolphins at Kumai Bay, Central Kalimantan, Indonesia. Unpublished Manuscript. Kasuya, T. 1999. Finless porpoise Neophocaena phocaenoides (G. Cuvier, 1829). Ridgeway, S.H. & Harrison, R. (eds.), In : Handbook of Marine Mammals. Volume 6 : The Second Book of Dolphins and Porpoises. Pp. 411-441. Academic Press, San Diego. Kleinenberg, S.E., Yablokov, A.V., Bel’kovich, B.M. & Tarasevich, M.N. 1969. Beluga (Delphinapterus leucas). Investigation of the species. Wiener Bindery, ltd., Jerusalem. Pp. 376. Translated from Russian. Lee, H. 1878. The White Whale. London. Lowry, L.F., Burns, J.J. & Nelson, R.R. 1987. Polar bear, Ursus maritimus, predation of belugas, Delphinapterus leucas, in the Bering and Chukehi Seas. Can. Field-Nat. 101: 141-146. Nelson, E.W., True, F.W. 1887. Mammals of Northern Alaska. Report upon Hist. Natur. Collect. made in Alaska. Arctic Ser. of Publ. 3, US Army. Parsons, E.C.M. & Wang, J.Y. 1998. A review of finless porpoises (Neophocaena phocaenoides) from the South China Sea. Proceedings of the Third International Conference on the Marine Biology of the South China Sea, Hong Kong, 28 October-1 November 1996 (ed. B. Morton). Hong Kong University Press. Perrin, W.F. 1989. Dolphins, porpoises and whales. An action plan for conservation of biological diversity: 1988-1992. 2nd ed. IUCN, Gland, Switzerland. Reeves, R.R., Wang, J.Y., & Leatherwood, S. 1997. The finless porpoise, Neophocaena phocaenoides (G. Cuvier 1829): a summary of current knowledge and recommendations for conservation action. Asian Marine Biology 14: 111-143. Reeves, R.R., Jefferson, T.A., Kasuya, T., Smith, B.D., Wang Ding, Wang, P., Wells, R.S., Würsig, B. & Zhou, K. 2000. Report of the workshop to develop a conservation Action Plan for the Yangtze River finless porpoise, Ocean Park, Hong Kong, 16-18 September 1997. In: R.R. Reeves, B.D. Smith, & T. Kasuya
8 General introduction in facultative river dolphins and Orcaella brevirostris
(eds.) Biology and Conservation of Freshwater Cetaceans in Asia. Pp. 67-80. IUCN/SSC Occasional Paper 23, Gland Switzerland and Cambridge, UK. Rudolph, P., C. Smeenk and S. Leatherwood, 1997. Preliminary checklist of cetacea in the Indonesian Archipelago and adjacent waters. Zoologische Verhandelingen. Leiden, Nationaal naturhistorisch Museum. Scheffer, V.B. & Slipp, J.W. 1948. The whales and dolphins of Washington State with a key to the cetaceans of the west coast of North America. Amer. Midl. Na. 39: 257-337. Smith, T.G. 1985. Polar bears, Ursus maritimus, as predators of belugas, Delphinapterus leucas. Can. Field-Nat. 99: 71-75. Stoner, D. 1938. New York State records for the common dolphin, Delphinus delphis. N.Y. State Mus. Circ. 21: 1-16. Suwelo, I.S. 1988. Whales and whaling in Indonesia. Paper submitted to the Indian Ocean Sanctuary Administrative Meeting of the International Whaling Commission, Canberra, 18-20 May. True, F.W. 1889. Contributions to the natural history of the cetaceans: A review of the family Delphinidae. Bull. U.S. Nat. Mus. 36: 192 p. Vlaykov, V.D. (1944) Chasse, biology et valeur économique du Marsouin Blanc ou Béluga (Delphinapterus leucas) du fleuve et du golfe Saint-Laurent. Ph.D. Département des pêcheries, Quebec, contribution No. 14: 194 p.[ In French]. Warhol, P. 1986. Humprey. Whalewatcher 20: 13-15.
9 Chapter 1
10 Preliminary observations of the Irrawaddy Dolphin in the Mahakam River
CHAPTER 2
Observations on the occurrence of the Irrawaddy Dolphin, Orcaella brevirostris, in the Mahakam River, East Kalimantan, Indonesia
Zeitschrift für Säugetierkunde 64, pp. 54-58, 1999 (with additions)
In order to collect information of the dolphin (seasonal) distribution range, fish abundance and threats, interviews with fishermen and residents throughout the range were held.
11 Chapter 2
ABSTRACT
A two-months’ preliminary survey by boat was conducted on a population of Irrawaddy dolphins Orcaella brevirostris in the Mahakam River in East Kalimantan, Indonesia in 1997 in order to assess total dolphin distribution range and encounter rates. Dolphins were not homogeneously distributed over the entire river length and over different habitats. Significantly higher encounter rates were found in the middle river section between Muara Kaman (c. 200 km from the mouth) and Long Iram (c. 490 km from the mouth) compared to the lower and upper river sections. This section presumably forms the primary habitat for the dolphins, at least during medium to low water levels when this survey was conducted. Encounter rates are just as low to those reported for the critically endangered Yangtze River dolphin, Lipotes vexilifer and indicate the critical situation of this population. Various factors seem to degrade their habitat and more intensive research to monitor total population abundance is required in order to reassess their status.
RINGKASAN
Dua bulan survei awal dengan menggunakan kapal untuk meneliti populasi lumba- lumba Irrawaddy Orcaella brevirostris di Sungai Mahakam, Kalimantan Timur, Indonesia pada tahun 1997 untuk memperkirakan jangkauan penyebaran dan mencari rata-rata. Lumba-lumba penyebarannya tidak merata sepanjang sungai dan pada habitat yang berbeda. Rataan penemuan yang lebih tinggi ditemukan di bagian tengah sungai antara Muara Kaman (c. 200 km ke hulu) dan Long Iram (c. 490 km ke hulu) dibandingkan dengan bagian hilir dan hulu sungai. Bagian ini mungkin merupakan habitat utama untuk lumba-lumba, setidaknya selama permukaan air sedang sampai permukaan air rendah pada saat survei ini dilakukan. Rata-rata penemuan sama kecilnya dengan yang dilaporkan pada lumba-lumba yang terancam kepunahan di Sungai Yangtze, Lipotes vexilifer dan menunjukkan kritisnya keadaan populasi ini. Banyak faktor-faktor yang nampaknya semakin mengurangi habitat mereka dan diperlukan penelitian yang terus- menerus untuk mengawasi keseluruhan jumlah populasi dengan tujuan untuk mengetahui kembali status mereka.
12 Preliminary observations of the Irrawaddy Dolphin in the Mahakam River
The Irrawaddy dolphin, Orcaella brevirostris (Gray, 1866), is considered a ‘facultative’ river dolphin of which distinct riverine and coastal, marine populations exist. The species is mainly found in shallow coastal waters of the tropical Indo-Pacific, but also in major river systems, in particular: Irrawaddy, Mekong, Mahakam, and the estuaries of the Ganges and Brahmaputra (Thomas, 1892; Lloze 1973; Leatherwood et al., 1984; Marsh et al., 1989). Relatively few published studies exist pertaining specifically to the population of Irrawaddy dolphins, in the local vernacular referred to as Pesut, in the Mahakam River, East Kalimantan, Indonesia. Studies so far have focused on the distribution and daily movement pattern of the species in Semayang-Melintang Lakes and connecting Pela and Melintang tributaries (Priyono, 1994) and on bioacoustics (Kamminga et al., 1983). Although no systematic surveys on their abundance have been conducted so far, the Indonesian Directorate General of Forest Protection and Nature Conservation reported the existence of a population of 100-150 individuals for Semayang Lake, Pela River, and adjacent Mahakam River (Tas’an & Leatherwood, 1984) while an unpublished estimate of 68 individuals in the Mahakam River was reported by Priyono in 1993. In this study, I present results of a preliminary survey, which was conducted on the Mahakam River, its tributaries and adjacent lakes in East Kalimantan, Indonesia. Two surveys were conducted, both at medium to low waterlevels, the first from 27 February till 9 March 1997 and the second from 21 March till 6 April 1997. The river was surveyed using a small motor boat, occasionally by large public boat and by large and small motorized canoes, from Muara Kaman (ca. 200 km upstream) to Burit Halau, at the rapids past Long Bagun (ca. 600 km upstream). In addition, the Semayang, Melintang and Jempang Lakes were surveyed as well as the Pela, Melintang, and Kedang Pahu tributaries. The total survey length was 1085 km. For analysis of sighting frequencies, the river was divided into a lower (from Samarinda, ca. 100 km upstream, until Muara Kaman, middle (from Muara Kaman until Long Iram, ca. 490 km upstream), and upper section (from Long Iram until the rapids after Long Bagun). Tributaries and lakes surveyed were also analysed separately. Encounter rates were calculated for each section by dividing the number of observed dolphins by the number of kilometers searched. For testing whether the sighting frequencies are homogeneously distributed over all sections, and whether significant differences exist between different sections, G-tests of goodness of fit for single classification frequency distributions were used. To obtain a better 2 approximation to x , Williams’ correction to G was applied (Gadj; Sokal & Rohlf, 1981). G values were compared with critical values of the chi-square distribution (table C in Siegel & Castellan, 1988). Because multiple tests were performed, a corrected alpha of 0.01 was used in place of the nominal alpha of 0.05 (Rice, 1989). Dolphins were spotted by eye and by means of binoculars. Group composition, location, diving times, respiration rates and behaviors were recorded and photos taken. Additional data on the occurrence and status of Pesut were collected by interviewing local inhabitants, mainly fishermen.
13 Chapter 2
14 Preliminary observations of the Irrawaddy Dolphin in the Mahakam River
During the present study, a total of 32 dolphins were observed, of which four were juveniles. During the first survey 29 individuals were encountered while during the second only 3 were observed, presumably because more time was spent in the upper section of the Mahakam, where no dolphins were observed. Group size varied from 3 to 7 animals with a median group size of 4 individuals. No minimum estimate of abundance could be made as only three dolphins were identifiable individually on the basis of their dorsal fin (no systematic photos of their dorsal fin were made). Also, there is the possibility that the dolphins might have been encountered more than once during each survey, in case they were heading in the same direction during the night as we were heading during the day. Irrawaddy dolphins were found to be rather inconspicuous; they do not leap high out of the water and may stay submerged for up to 12 minutes, surfacing only briefly. Except for some noises produced with their blow holes, which could be heard over 100 m distance, no audible whistles or pure tones were heard. Pesut appeared to be very social, continuously staying in close contact with one another, regardless of whether they were milling (feeding), travelling, or resting. Table 1 shows the encounter rates, i.e. the number of dolphins per km of river searched, for different sections of the Mahakam River sytem. The dolphins are not homogenously distributed over the whole length of different river sections, tributaries and lakes (Gadj=47.8, df=4, p<0.01). The encounter rates of the middle river section are significantly higher than those of the upper section (Gadj=39.2, df=1, p<0.01). Significantly higher encounter rates were also found for the tributaries when compared to the combined main river sections (Gadj=8.3, df=1, p<0.01). However, all tributary observations of Pesut were made in the relatively short Pela tributary (only 8 km search effort), a connecting tributary to Semayang Lake and the Mahakam River. No sightings were made in the longer tributary Kedang Pahu of which 65 km in total was searched. No significant differences were found between encounter rates of middle river section and tributaries. As all tributary observations were made in the Pela tributary connecting to the middle section of the main river, and observations in the middle section of the Mahakam were significant higher than in the upper section (with a higher search effort), this section presumably forms the primary habitat for the dolphins, when water levels are medium to low.
Table 1. Encounter rates - dolphins observed per km of river searched.
Section Search effort No. of Encounter rate (km) individuals No. of individuals/ km Lower River Section 20 0 0 Middle River Section 432 25 0.06 Upper River Section 505 0 0 Tributaries 78 7 0.09 Lakes 50 0 0
15 Chapter 2
Encounter rates for the Semayang and Melintang Lakes, though lower, were not significantly so, when compared to the combined rates of the river and tributaries (Gadj=3.9, G0.01=6.6). The significant difference in encounter rates between these sections is probably a result of treating dolphins sightings in the Pela tributary as tributary observations. However, the dolphins’ presence in either the Pela tributary or in Semayang Lake might depend on time of the day, as the dolphins are reported to migrate daily between these areas (Priyono, 1994). The absence of observations of dolphins in the lakes most certainly is due to the fact that only 50 km were surveyed of the 10.300 hectares and 8.900 hectares large Semayang and Melintang Lakes, respectively. No significant differences in encounter rates were found between lower and other river sections, possibly due to the low search effort in this section. The encounter rates found for Orcaella brevirostris in the Mahakam River are in the same order of magnitude as that reported for Lipotes vexilifer in the Yangtze River (0.09 dolphins/ km), a population considered to have a high exctinction risk (Hua & Chen, 1992). However, the encounter rate of 0.06 dolphins/ km in the mainstem Mahakam River, is considerably lower than those recorded, at similar medium-low water level conditions, for Inia geoffrensis and Sotalia fluviatilis in the mainstems of the Amazon-Marañon-Ucayali (0.18 and 0.27 dolphins/ km, respectively; Leatherwood, 1996). In the present study, Pesuts were observed up till Tering, 400 km upstream (Fig. 1), but they are said to occur up till the waterfalls after Long Bagun. Although no sightings were made in any of the lakes visited, Pesut has frequently been recorded in Semayang and Melintang Lakes (Tas'an & Leatherwood, 1984), but the dolphins are said to be absent from JempangLake. Whether the Pesut occurs between Samarinda (near the mouth of the river) and the open sea, and in which of the river's tributaries, remains unclear. When water levels are high, dolphins are often observed by local inhabitants high up the Kedang Pahu tributary, past the village of Damai. Although the dolphins at always moved away from our research vessel, they were observed twice near two villages (Muara Pahu and Tering) with high levels of boat traffic. According to local fishermen, they were said to frequent these places almost on a daily basis, presumably because of the higher availability of fish. In conclusion, the results from this preliminary survey seem to indicate that encounter rates of the Irrawaddy dolphin in the Mahakam River are relatively low and fall in the same class of those recorded for the seriously threatened Lipotes vexilifer. Furthermore, middle sections of the river seems to be the primary habitat of Pesut, at least at medium to low water levels. Given the many factors contributing to possible deterioration of dolphin habitat (e.g. pollution from mining, forest fires, logging and siltation), these observations of low encounter rates merits further study.
16 Preliminary observations of the Irrawaddy Dolphin in the Mahakam River
ACKNOWLEDGEMENTS
I wish to thank the East Kalimantan nature conservation authorities, sub Balai Konservasi Sumber Daya Alam, WWF-Indonesia and WWF-Netherlands for their support and cooperation. My special thanks to Ir. A.M. Rachmat, D. Suprijono, F. Butcher and boatsman Pak Sega, which all participated in the survey. I would like to thank Dr P.J.H. van Bree for all his help and support throughout the study, as well for his comments on the manuscript. Dr. C.J. Hazevoet, Dr A.Ø. Mooers, V. Nijman and an anonymous reviewer are also thanked for their comments on this manuscript. I. Lysenko and the World Centre for Monitoring Cambridge are thanked for drawning of the map.
REFERENCES
Christensen, M.S. 1992. Investigations on the ecology and fish fauna of the Mahakam River in East Kalimantan (Borneo), Indonesia. Int. Revue gesamt. Hydrobiol. 77: 593- 608. Hua, Y., Chen, P. 1992. Investigation for impacts of changes of the lower reach of Gezhou Dam between Yichang and Chenglingji on the Baiji, Lipotes vexilifer after its key water control project founded. J. Fish. China 16: 322-329. Leatherwood, J.S. 1996. Distributional ecology and conservation status of river dolphins (Inia geoffrensis and Sotalia fluviatilis) in portions of the Periuvian Amazon. Diss. thesis, Texas University, Texas. Leatherwood, S., Peters, C.B. Santerre, R.. Clarke, J.T. 1984. Observations of cetaceans in the northern Indian Ocean Sanctuary, November 1980-May 1983. Rep. Int. Whal. Commn. 34 : 509-520. Lloze, R.. 1973. Contributions a l’étude anatomique, histologique et biologique de l’Orcaella brevirostris (Gray -1866) (Cetacea-Delphinidae) du Mekong. Diss. thesis Toulouse, France. MacKinnon, K.; Hatta, G.; Halim, H.; Mangalik, A. 1996. The ecology of Kalimantan. Indonesian Borneo. Ecol. Indonesia series 3: 152. Marsh, H., Lloze, R., Heinsohn, G.E., Kasuya, T. 1989. Irrawaddy Dolphin Orcaella brevirostris (Gray, 1866). In: H. Ridgeway and R.J. Harrison (eds.), Handbook of marine mammals. River dolphins and the larger toothed whales 4. Pp. 101-118. Priyono, A. 1994. A study on the habitat of Pesut (Orcaella brevirostris Gray, 1866) in Semayang-Melintang Lakes. Media Konservasi 4: 53-60. Rice, W.R. 1989. Analyzing tables of statistical tests. Evolution. Int. J. Org. Evol. 43: 223-225. Siegel, S., Castellan, N.J., Jr. 1988. Nonparametric statistics for the behavioral sciences. Second edition, McGraw-Hill , Inc. Sokal, R.R.; Rolf, F.J. 1981. Biometry. The principles and practice of statistics in biological research. Second edition, W.H. Freeman and company, New York.
17 Chapter 2
Thomas, O. 1892. Viaggio di L. Fea in Birmania e regioni vicine. XLI. On the Mammalia collected by Signor Leonardo Fea in Burma and Tenasserim. Annali del Museo Civico di Storia Naturale di Genova 1892: 913-949. Tasa’n & Leatherwood, S. 1984. Cetaceans live-captured for Jaya Ancol Oceanarium, Djakarta, 1974-1982. Rep. Int. Whal. Commn. 34: 485-489.
18 Coastal cetacean diversity and habitat preferences in East Kalimantan
CHAPTER 3
Cetacean diversity and habitat preferences in tropical waters of East Kalimantan, Indonesia
Daniëlle Kreb and Budiono
Submitted manuscript
Two Gray’s (pantropical) spinner dolphins, Stenella longirostris with distinctive tripartite color pattern, photographed in the Berau Archipelago, October 2003. Photo: Budiono.
19 Chapter 3
ABSTRACT
East Kalimantan was chosen as a site to investigate cetacean diversity because of its probability as a migratory pathway for cetaceans from the Pacific to the Indian Ocean through the Sulu-Sulawesi Seas and Makassar Straits. The Berau Archipelago in the northeast of East Kalimantan Province provided the highest species richness and cetacean abundance (0.64 individuals/ km searched) compared to two other coastal areas of equal coastline length and nearly similar area size in East Kalimantan. A total of 10 species and subspecies were found along the entire coastline (total study area is 8.538 km2) of which 8 were found in the Berau Archipelago (minimum area size is 170 km2). High cetacean diversity in this area is due to the abundant islands and reefs, in which habitat 60% of all taxa were encountered and which had the highest relative cetacean abundance (0.82 individuals/ km searched) of all habitat types, i.e., offshore and near shore waters, bay and delta. Most sightings were made within 5 km of islands and reefs, so a 5-km-radius protection zone off islands and major reefs may be one conservation recommendation. First sighting records (4) for Indonesia of Stenella l. roseiventris were made.
RINGKASAN
Kalimantan Timur telah dipilih sebagai tempat untuk penelitian keanekaragaman cetacean sebab kemungkinan besar daerah ini digunakan sebagai jalur berpindahnya cetacean dari Laut Pasifik ke Laut Hindia melalui Laut Sulu-Sulawesi dan Selat Makasar. Kepulauan Berau di timur laut Provinsi Kalimantan Timur menyimpan banyak kekayaan dari segi jenis dan jumlah (0,64 ekor/km yang diteliti) dibandingkan dengan dua perairan laut lainnya dengan panjang garis pantai dan ukurannya yang hampir sama di Kalimantan Timur. Sejumlah 10 jenis dan sub jenis ditemukan disepanjang garis pantai (Total daerah studi 8.538 km2), dimana 8 diantaranya ditemukan di Kepulauan Berau (ukuran daerah minimum 170 km2). Tingginya keanekaragaman cetacea di daerah dikarenakan oleh banyaknya pulau dan karang, dimana 60 % habitat dari seluruh jenis ditemukan dan relatif memiliki jumlah cetacea tertinggi (0,82 ekor/ km penelitian) dari seluruh tipe habitat, seperti lepas pantai dan perairan dekat pantai, teluk dan delta. Kebanyakan penampakan terjadi dalam jarak 5 km dari pulau and karang, jadi dalam area radius perlindungan 5 km dari pulau dan karang besar dapat menjadi satu rekomendasi untuk konservasi. Catatan pengamatan yang pertama kali (4) untuk Stenella I. roseiventris di Indonesia dibuat.
20 Coastal cetacean diversity and habitat preferences in East Kalimantan
INTRODUCTION
The coastal waters of East Kalimantan form the western part of the Indo-West Pacific centre of maximum marine biodiversity (Voris, 2000). Historical and ecological perspectives support this hypothesis. During the last ice age (17,000 yrs ago), sea level was situated 120 m lower than now (MacKinnon, 1997). Shelf seas, e.g., the Java Sea, had disappeared and Kalimantan was part of the South East Asian continental mainland. The Indonesian through-flow (Gordon & Fine, 1996) continued to pass east of Kalimantan, through the Sulu-Sulawesi Seas and Makassar Strait carrying larvae and plankton from the Pacific to the Indian Ocean. Similarly, these seas most likely represent a migratory pathway for whales and dolphins. East Kalimantan has a wide range of habitats such as major rivers, deltas, mangroves, island/ reefs and deepwater offshore habitat, which are all inhabited by cetaceans. The Indonesian Archipelago contains some 5 million km2 of territory (including water and land), of which 62% consists of seas within the 12-mile coastal limit (Polunin, 1983). At least 29 species of cetaceans are reported to occur in the seas of the Indonesian Archipelago (Rudolph et al., 1997). However, only a few dedicated studies have been conducted on the abundance, distribution and conservation of cetaceans in Indonesia. Cetaceans are threatened with local extinction in many parts of the world, but nowhere more obviously than in Asia (Reeves et al., 1997). Growing human populations are putting an increasing pressure on natural resources including the stocks of wild fish and crustaceans, supplies of freshwater, and even coastal landscapes themselves, e.g., through ‘reclamation’ projects, harbor construction, mariculture and oil spills. Rivers, estuaries and coastal marine waters are becoming increasingly unhealthy ecosystems for wildlife. Modifications and degradations of the habitats of dolphins and porpoises have often resulted in dramatic declines in their abundance and range (Reeves et al., 1997). The present survey involves a preliminary assessment of cetacean diversity in the waters off the East Kalimantan coast and provides the basis for future conservation- orientated research on cetaceans in this area. The objectives of the preliminary survey were to assess the diversity and occurrence of cetaceans and identify important cetacean areas in terms of species richness and abundance.
METHODS
Survey area
Near-shore and (island) offshore waters were surveyed along a total strip of 700 km of coastline. This coastline was divided into three survey areas of equal length, ca. 230 km (Fig. 1). Survey area 1 in the south included Balikpapan Bay (mangrove), near- shore waters, and the inner and outer Mahakam Delta area (mangrove). Total survey
21 Chapter 3
2o
Berau Delta Survey Area 3
Kaniungan Islands
EAST KALIMANTAN o Mangkaliat 1 Sangkulirang Peninsula Bay
Survey Area 2
0 23 46 0o
Mahakam Delta
Survey Area 1
o Balikpapan 1 Bay o o o 117 118 119
Figure 1. Map of survey areas along the East Kalimantan coastline, Indonesia.
22 Coastal cetacean diversity and habitat preferences in East Kalimantan
area was 2467 km2. The shallow, near-shore strip (< 20 m depth) is quite wide (>5 km <10 km). Survey area 2 had an area of 2732 km2 and included the near-shore waters north of the Mahakam Delta, small delta areas of minor rivers, Sangkulirang Bay (mangrove) and offshore island reefs as far as the Mangkaliat Peninsula. The shallow coastal strip was very narrow (on average < 1 km) in the area north of the Mahakam Delta until Sangkulirang Bay and even narrower along the coast farther eastwards to the Mangkaliat Peninsula (< 100 m). Survey area 3 included the Berau Archipelago with an area of 3339 km2, which contains a high density of islands and reefs, the Berau Delta (mangrove), near- shore waters (>2 km < 4 km north of Kaniungan Islands and < 100m from Mangkaliat Peninsula until Kaniungan Islands) and offshore deepwater habitat (< 900 m deep). The southern Mangkalihat Peninsula narrows the passage between Sulawesi Island and Borneo Island and a shallow shelf is absent.
Field methods
Cetaceans were visually searched for along a strip of 700 km of coastline during vessel-based surveys in six different survey periods, each lasting two weeks on average between May 2000 and October 2003. Total search effort by boat was 4481 km (362 h) during 80 days. Area 1 was surveyed during all seasons (governed by winds from all directions), whereas area 2 was surveyed during eastern wind (calm sea) conditions and area 3 during a transition period from south-western to northern wind conditions with days of mirror-like sea surface alternated with days of beaufort 5 sea state. Only sightings made during days with an average beaufort sea-state of 3 or less were used for relative abundance analysis. Pre-determined survey transects were designed to provide representative survey coverage of various habitats. Searches were conducted alternatively from 2 wooden boats of different lengths, i.e., 16 m and 12 m, and horsepower 16 hp and 26 hp respectively, depending on sea conditions and habitat. When surveying deep, offshore waters and remote survey areas, the latter boat was used, which had an additional outboard engine and was used only off-effort for a fast return to shore. The 3-person- observer team followed a routine survey protocol for observation and data recording, in which the first observer scanned continuously with 7x50 binoculars, the second observer searched for dolphins unaided, and recorded all sighting effort data and environmental and geographical conditions using a GPS every 30 minutes, and the third observer searched at the rear by unaided eye and occasionally used binoculars. Positions changed every 30 minutes. One transect was surveyed in one day, and double sightings on the same transect were avoided. Upon making a sighting, radial distance between boat and dolphins was estimated, and compass bearing of the boat and of the dolphins and coordinates of the sighting location were recorded. Species were then identified. If more than one species was observed, it was recorded whether the multiple species mixed. If the
23 Chapter 3
species did not mix, the mean distance between the single-species groups was recorded. Minimum, maximum and best estimates were made of group size and of the number of calves and juveniles. We attempted to photograph each sighting for confirmation of species identification. Depth at sighting location was determined from an official sea map of the area for study area 3. For the other two study areas, a fish finder was used for depth measurement.
Table 1. Encounter rates of individual cetacean species by habitat type and habitats combined in decreasing order of abundance.
Encounter Mean depth Search rateb (r) Sighting (m) of Mean effort (dolphins/ Mean (Sub)species habitat sightings na G (km)2 km) r Tursiops truncatus offshore 172 (50-400) 6 18 261 0.291 island/ reefs 103 (5-300) 6 13 537 0.204 0.248 Stenella attenuata island/ reefsc 280 1 55 261 0.210 0.210 Stenella longirostris offshored 365 (300-400) 2 45 537 0.168 0.168 Stenella longirostris, sp. offshore 50 1 45 537 0.083 (with short beak)e islands 75 (35-115) 2 28 261 0.107 0.095 Orcaella brevirostris near shore 6.9 (2-23) 18 3 1616 0.029 delta 5.6 (3-10) 5 4.8 1010 0.019 0.085 bay 14.3 (2.5-30) 67 3.4 1057 0.220
Stenella l. roseiventris near shore 23 1 2 1616 0.002 offshore 260 (50-400) 3 10.7 537 0.060 0.030 island 35 1 8 261 0.030 Tursiops sp. nearshore6 12.5 (11-14) 4 9 1616 0.028 0.028 Pseudorca crassidens island 400 1 7 261 0.027 0.027 Peponocephala electra island 400 1 4 261 0.015 0.015 Globicephala macrorhynchus island 280 1 4 261 0.015 0.015 Tursiops aduncus offshore 350 1 7 537 0.013 0.013 Neophocaena phocaenoides near shore 6.3 (2-10) 3 4.7 1616 0.009 0.009 a = number of groups sighted b = habitat specific search effort c = > 20 m depth coastal contour line, > 5 km distance off islands and reefs d = < 20 m depth coastal contour line, > 5 km distance off islands and reefs e = tentative identification of possible sub-species of Stenella longirostris f = < 5 km distance of islands and reefs
24 Coastal cetacean diversity and habitat preferences in East Kalimantan
RESULTS
Species identification
A total of 112 independent sightings were made in the 700-km long- survey strip (20 20’ N, 1190 E – 10 50’ S, 116050 E) in a total survey area of 8.538 km2 (Fig. 1). A total of 868 individual cetaceans of 9 different species, one sub-species and one additional tentatively identified sub-species were encountered (Table 1). Five sightings of the dwarf spinner dolphin sub-species, Stenella l. roseiventris, represent the first records for Indonesia and first record of occurrence for the Sundai region1 (Fig. 2). The dwarf spinner dolphins were estimated to be ¾ the size of the more pelagic Gray’s dolphin, Stenella l. longirostris. Their colour pattern (consisting of two elements) was as dark-gray as for bottlenose dolphins, Tursiops truncatus. Near the abdomen, a not very distinct layer of lighter dark-gray was visible. They lacked the tripartite base pattern and distinct pectoral stripes of the larger pelagic spinner dolphins that we observed. Juvenile dwarf spinner dolphins were also observed. The dwarf spinner dolphins usually moved in small groups (mean n = 8 individuals) and were observed in mixed aggregations (within 30 m distance) in three out of five sightings. In the sightings with Gray’s spinner dolphins, their group formation remained in tact. During the other two sightings the dwarf spinner dolphins were observed in close proximity with other species but did not mix, i.e. the distance between different species was more than 30 m. Three sightings were made in deep water (50-400 m) but in relatively close proximity to islands (< 10 km). Three sightings were made of a variant form of larger pelagic spinner dolphins; these had a shorter beak and may represent an un-described sub-species. These were identified during one single-species sighting, one mixed aggregation with dwarf spinner dolphins and spotted dolphins, Stenella attenuata, and one sighting in close proximity (ca. 100 m) to dwarf spinner dolphins and bottlenose dolphins. Their mean group size was 34 individuals. One sighting was made of a small group of dolphins tentatively identified as Indo- Pacific bottlenose dolphins, Tursiops aduncus (n = 7 individuals), which could be distinguished from common bottlenose dolphins by having a more slender body, longer beak and slightly smaller body size. This small group occurred in area 3 in a mixed species group with an average distance of ca. 50 m from common bottlenose dolphins and ca. 50 m distance from spinner dolphins, which occasionally approached. General bottlenose behaviors included slow travel, milling and feeding, and there were many small tuna in the area. The remaining Tursiops sightings in area 2 and 3 were made near islands and reefs, and offshore waters, and appear to have been of T. truncatus. In area 1, Tursiops sightings were made near-shore, but no positive
1 This dwarf form of spinner dolphins was first described by Wagner 1846 as Delphinus roseiventris based on a specimen from the Arafura Sea in Indonesia. Later specimens were collected from the Mollucas.
25 Chapter 3
Figure 2. Three dwarf spinner dolphins, Stenella l. roseiventris with obscure, lateral color pattern, photographed in the Berau Archipelago, October 2003. Photo: Budiono.
species identification could be made, so all the bottlenose dolphin sightings in this area are referred to as Tursiops sp. No unidentified sightings were made.
Relative species abundance and habitat occurrence
The most abundant species observed was the common bottlenose dolphin (0.25 dolphins per habitat specific search effort in km). Other commonly observed species were the pantropical spotted dolphin (0.21 dolphins/ km) and the spinner dolphin (0.17 dolphins/ km). However, the spotted dolphin was only sighted once, but in a large group of 55 individuals. The species least frequently observed were the finless porpoise, Neophocaena phocaenoides, and the Indo-Pacific bottlenose dolphin (0.009 & 0.013 dolphins/ km, respectively). The cetaceans occurred in five different habitat types: near-shore (< 20 m depth coastal contour line, > 5 km off islands and reefs), offshore (> 20 m depth
26 Coastal cetacean diversity and habitat preferences in East Kalimantan
coastal contour line, > 5 km off islands and reefs), bay, delta, and islands/ reefs (< 5 km from islands and reefs). The dwarf spinner dolphin, common bottlenose dolphin, and the Irrawaddy dolphin, Orcaella brevirostris, had the most variable habitat occurrence as each species occurred in three marine habitat types. The latter species actually occurred in 4 habitat types if one includes the freshwater habitat (Mahakam River). Depths at sighting locations varied between a minimum of 2 m, recorded for finless porpoises and Irrawaddy dolphins in near-shore habitat, and a maximum of 350-400 m, recorded for spinner dolphins, dwarf spinner dolphins, bottlenose dolphins, Indo-Pacific bottlenose dolphins, false killer whales (Pseudorca crassidens) and melon-headed whales (Peponocephala electra) in island and offshore habitat.
Relative cetacean abundance by habitat and survey area
The habitats with highest relative abundance of cetaceans were island and reef (0.82 dolphins/ km searched), followed by, offshore (0.529 dolphins/ km) and bay (0.219 dolphins/ km) (Table 2). Delta and near-shore areas were rather poor by comparison (0.023 & 0.071 dolphins/ km, respectively). Near-shore areas and offshore habitats were moderately rich in species occurrence (both 40% of total number species encountered). Island/ reef habitats had the highest species richness (60% of total no. species). The bays and delta habitats were only frequented by one species, the Irrawaddy dolphin. Coastal Irrawaddy dolphins in and near the Mahakam delta were sighted offshore of the delta at low tide, whereas one inshore sighting at 10 km upstream of the mouth was made at high tide. The mean salinity of 12 ppt (SD = 10; range = 4.6-19.3 ppt) measured at dolphin positions in the delta is associated with brackish waters.
Table 2. Number of individuals and cetacean species encountered in different habitats.
Habitat Survey Total no. Encounter No. of % of total no. of effort (km) individual rate (sub)species (sub)species cetaceans (Dolphins/ (n = 10)a km) Bay 1057 231 0.219 1 10 Delta 1010 24 0.023 1 10 Near shore 1616 115 0.071 4 40 Offshore 537 284 0.529 4 40 Islands/ reefs 261 214 0.820 6 60 Total 4481 868 a = tentative identification of the variant form of Gray’s spinner dolphin with short beaks is excluded.
Relative cetacean abundance also varied by survey area: survey area 3, the Berau Archipelago, scored both the highest encounter rate (0.64 individuals/ km
27 Chapter 3
searched in area 3) as well as highest species richness, i.e., 8 species, which was 2.7 times higher than species richness in the other two areas, whereas the area surveyed was only 1.2 and 1.3 times larger than the other areas (Table 3). The minimum area size within which all 8 species of this area were found was ca.170 km2.
Table 3. Diversity of cetacean (sub-)species and relative individual- and species abundance per survey area.
Survey (Sub)species Surveyed Search Encounter Survey area Species areas habitats effort (km) rate (km2) richnessa (dolphins /km) Area 1 Neophocaena phocaenoides Near shore; 3216 0.12 2467 3 Orcaella brevirostris bay; large delta Tursiops sp. (outer & inner)
Area 2 Orcaella brevirostris Near shore; 549 0.21 2732 3 Stenella l. roseiventris bay; small delta; Tursiops truncatus offshore; islands Area 3 Globicephala Near shore; 714 0.64 3339 8 macrorhynchus large delta Pseudorca crassidens (outer); Peponocephala electra offshore; Stenella attenuata islands Stenella longiristris Stenella longirostris sp Stenella l. roseiventris Tursiops aduncus Tursiops truncates
_ (underline) = habitat in which dolphins were sighted a = including the sub-species Stenella l. roseiventris
Table 4. Mixed species sightings n Mixed species sightings (+ dependent sightings) Groups mixing or not?a
1 Neophocaena phocaenoides; Orcaella brevirostris mixing 2 Orcaella brevirostris; Stenella l. roseiventris not mixing; moving in other directions 3 Stenella longirostris; Stenella l. roseiventris; Tursiops truncatus; all species mixing Tursiops aduncus 4 Stenella longirostris, sp.; Stenella l. roseiventris; Tursiops truncatus not mixing; > 100 m distance among each species 5 Stenella longirostris, sp.; Stenella l. roseiventris; Stenella attenuata all species mixing 6 Pseudorca crassidens; Peponocephala electra mixing 7 Globicephala macrorhynchus; Stenella attenuata not mixing; > 30 m distance among each species 8 Stenella longirostris; Stenella l. roseiventris mixing n = independent sightings during which more than one species was encountered a = groups were considered to mix if the distance between different species was less than 30 m
28 Coastal cetacean diversity and habitat preferences in East Kalimantan
Species composition of sightings
Sightings of mixed species involved 20% (n = 8) of all sightings in habitats where more than one species were observed (n = 40) (Table 4). However, the percentage of sightings of groups which actually mixed was 12.5% (n = 5). The remaining 7.5% (n = 3) involved dependent sightings of groups, which did not mix (minimum distance range = 30 m & 100 m). All identified species mixed at least once with other groups, except for the short-finned pilot whale (n = 10 = 91% of all species). Dwarf spinner dolphins were most often sighted in mixed-species aggregations (n = 3), followed by spinner dolphins (n = 2), whereas all other species were seen to mix only once. Although Indo-Pacific bottlenose dolphins were observed at a close distance (15-20 m) from common bottlenose dolphins, they remained in group formation. In all sightings of mixed groups the different species of dolphins were within close range of each other, but they maintained their own group formation.
DISCUSSION
Species identification
Although dwarf spinner dolphins are usually associated with shallow in-shore waters (Perrin et al., 1999), the observation in deep waters in the Berau Archipelago is not so unusual since the area is very rich in islands and reefs, and deeper waters are interspersed with shallow reefs. Also, all deep-water sightings in this study were made within 10 km of islands and reefs. The dwarf spinner dolphins observed in this area share some characteristics with small spinner dolphins occurring in the Arabian Sea of Oman (Waerebeek et al., 1999) and the Aden Gulf of the Republic of Djibouti (Robineau & Rose, 1983), mainly in size with both forms is the smaller body size in comparison to pantropical (Gray’s) spinner dolphins. Also, one of the two forms of spinner dolphins described for Oman has a dark dorsal overlay, obscuring the tripartite base pattern as seen in pantropical spinner dolphins, and such a dark, not well-distinguished, pattern was also seen in the dwarf spinner dolphins in East Kalimantan. The belly in both had a lighter colour, although the form of Oman described above were pink-bellied, whereas the bellies of dwarf spinner dolphins were still gray-coloured. Pink colour in cetaceans occurring in very warm waters may be an ephemeral feature caused by physiological heat management. The dwarf spinners in East Kalimantan share the two-coloured pattern, a dark cape and slightly lighter pectoral and ventral side with the spinner dolphins in the Aden Gulf. The Indo-Pacific bottlenose dolphins appeared well distinguishable from common bottlenose dolphins, especially when they were encountered during the same sighting. The short-beaked form of spinner dolphins needs further study. However, the fact that these were identified during sightings when all individuals shared this trait, may indicate that this possibly represent a different form and perhaps a new sub-species. Also, the short
29 Chapter 3
beak form of spinner dolphins were never observed in mixed sightings with the pantropical-spinner dolphins. Photographic material may aid in the future identification of dwarf spinner dolphins, Indo-Pacific bottlenose dolphins and the short-beaked form of spinner dolphins in these waters.
Species richness
In spite of the fact that survey effort (km) in area 1 was 5 times as high as in the other areas and covered all seasons, species richness was 2.6 times lower than that found in area 3 and similar to that in area 2. Survey effort in areas 2 and 3 was only made during one season, so the species richness there is likely to be higher than recorded. Based on the relatively high species richness and presence of species with a restricted range and a globally conservation dependent status, the waters near the Berau Islands have both a local and global biodiversity importance. In comparison, 14 species of cetaceans were identified in Komodo (identified as one of the richest marine diversity sites in the Indo-Pacific) National Park waters (1,214 km2 surface waters) (Kahn et al., 2000), whereas in the Berau study area alone, 8 species were encountered in an area of only ca. 170 km2. Although there are undoubtedly other areas of high cetacean diversity in Indonesia, such as reported for Solor and Lembata Island in eastern Indonesia (Weber, 1923; Barnes, 1980; Hembree, 1980), there are no comparative data on local species richness available. Most likely only a proportion of the actual numbers of species that occur in the Berau Archipelago seasonally or year round were observed in this preliminary survey, so the species richness may be even higher.
Conservation recommendations
We found that most sightings and species occurred within 5 km of islands and reefs, so a 5-km-radius protection zone off islands and major reefs may be one conservation recommendation. Otherwise, the restricted range of 170 km2 within which 8 identified cetacean species in the Berau Archipelago were observed has a good conservation potential to become a marine vertebrate sanctuary. The area also hosts a number of shark and turtle species, and during the present survey a sighting of a large group of manta rays, Manta birostris, was made (65 individuals). Also, one dugong, Dugong dugon, was observed. The area also includes four islands that are frequently visited by tourists, so the area has a high potential for eco-tourism. However, any intended dolphin/ whale watching should be controlled and guided by instructed and responsible boat operators. The second area in East Kalimantan coastal waters that is recommended as a conservation site is Balikpapan Bay. A high density of Irrawaddy dolphins (0.22 dolphins/ km search effort) was observed in the bay, as well as occasional sightings of individual dugongs. Just 1 to 10 km outside the bay bottlenose dolphins and finless
30 Coastal cetacean diversity and habitat preferences in East Kalimantan
porpoises were observed in shallow waters. Since in this study area four surveys were carried out in different seasons (northwestern wind; northern wind; southeastern wind; southern wind) and Irrawaddy dolphins occurred during all surveys in the bay, this area has a year-round importance. Besides the extensive sedimentation due to mangrove conversion, which has caused a decrease in sea grass fields and fish resources, and pollution (oil and mining exploitation, local city sewages), no other major threats have been detected for this area.
Research recommendations
Red List designation of three species, i.e., pantropical spotted dolphin, spinner dolphin, and short-finned pilot whale is Lower Risk (conservation dependent) (Reeves et al., 2003). Conservation status for all other species is Data Deficient. The status of the dwarf spinner dolphin has not been evaluated, but it has the most restricted range, being confined to shallow inner waters of Southeast Asia (Perrin et al., 1989; Rudolph & Smeenk 2002) although in this study the species also occurred in deepwater habitat near shore. The lack of data on the status of the species in this study indicates the need for more research to assess each species’ abundance, habitat quality, and fisheries interactions. The freshwater population of Irrawaddy dolphins in the Mahakam River is listed as Critically Endangered (Reeves et al., 2003). Freshwater Irrawaddy dolphins were sighted between 180 km and 480 km upstream of the mouth (Kreb, 2002), whereas the most inshore occurrence of coastal Irrawaddy dolphins is about 20 km upstream of the mouth at high tide according to interviews with fishermen. Since the coastal dolphins have not been sighted or reported to move further upstream than 20 km from the mouth and only enter the delta at high tide, they are considered to belong to a different, coastal stock than the true Mahakam River population, which is considered an isolated population. Future research is needed, focusing on the collection of biopsy samples and DNA analysis of coastal and freshwater Irrawaddy dolphins in order to clarify their status. Future survey effort should focus particularly on the Berau Archipelago and involve investigating which areas have a year-round or seasonal importance for all target species and relating this to ecological and bio-geographical factors. More extensive data than those yielded by the present rapid assessment survey (only two weeks) should be collected in this area during at least one year, covering all seasons. These data are needed to prepare a conservation action plan for all threatened target species and their habitats if degraded, possibly through establishment of protected marine parks and local education/ awareness campaigns and a long-term cetacean monitoring program.
31 Chapter 3
ACKNOWLEDGEMENTS
We thank the Indonesian Institute of Sciences (LIPI), East Kalimantan Nature Conservation Authorities (BKSDA Kaltim), Mulawarman University Samarinda (UNMUL) for providing permits and a counterpart during the survey period. We thank the fieldobservers Achmad Chaironi, Ahank, Arman, Audrie J. Siahainenia, Bambang Yanupuspita, Karen D. Rahadi, Muhamed Syafrudin, M. Syoim, Matthijs Couwelaar, Ramon, Rudiansyah, Sonaji, Syahrani and boat drivers Pak Iwan, Pak Johan, Pak Muis, Pak Kasino and Pak Anto. We would like to thank the following persons for their hospitality: Pak Djamhari and villagers at Derawan Island; conservation staff of Turtle Foundation at Sangalaki Island; villagers at Kaniungan Island. We are grateful for the support received during the study period from NWO/ WOTRO (Foundation for the advancement of tropical research), Ocean Park Conservation Foundation, Hong Kong; Martina de Beukelaar Stichting; Stichting J.C. van der Hucht Fonds; Gibbon Foundation; Netherlands Program International Nature Management (PIN/ KNIP) of Ministry of Agriculture, Nature Management and Fisheries; Van Tienhoven Stichting; World Wildlife Fund for Nature (Netherlands); Amsterdamse Universiteits Vereniging; Coastal Resource Management Program/ Proyek Pesisir. We thank the counterpart A. Arrifien Bratawinata, Frederick R. Schram, Peter J.H. van Bree, Chris Smeenk, Thomas A. Jefferson, Bert W. Hoeksema, Annelies Pierrot-Bults and the Plantage Library for their guidance, support and literature. William F. Perrin, Vincent Nijman and two anonymous reviewers are thanked for their corrections of the manuscript.
REFERENCES
Barnes, R. H. 1980. Cetaceans and cetacean hunting: Lamalera, Indonesia. Report on World Wildlife Fund Project 1428: 1-82. Gordon, A. L. & Fine, R. A. 1996. Pathways of water between the Pacific and Indian oceans in the Indonesian seas. Nature 379: 146-149. Hembree, E.D., 1980. Biological aspects of the cetacean fishery at Lamalera, Lembata. Report on World Wildlife Fund Project 1428: 1-55. Kahn, B., James-Kahn, Y. & Pet, J. 2000. Komodo National Park Cetacean surveys - A rapid ecological assessment of cetacean diversity, distribution and abundance. Indonesian Journal of Coastal and Marine Resources 3: 41-59. MacKinnon, K., Hatta, G., Halim, H. & Mangalik, A. 1997. The ecology of Kalimantan. The ecology of Indonesia series 3. Oxford University Press. Perrin, W. F., Dolar, M. L. L. & Robineau, D. 1999. Spinner dolphins (Stenella longirostris) of the western Pacific and South East Asia: pelagic and shallow-water forms. Marine Mammal Science 15: 1029-1053. Reeves, R. R., Wang, Y. J. & Leatherwood, S. 1997. The Finless Porpoise, Neophocaena
32 Coastal cetacean diversity and habitat preferences in East Kalimantan
Phocaenoides (G. Cuvier, 1829): A summary of current knowledge and recommendations for conservation action. Asian Marine Biology 14: 111-143. Reeves, R. R., Smith, B. D., Crespo, E. A. & Notarbartolo di Sciara, G. 2003. Dolphins, whales and porpoises: 2002-2010 conservation action plan for the world’s cetaceans. IUCN/SCC Cetacean Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK. Polunin, N. V. C. 1983. The marine resources of Indonesia. Oceanography and Marine Biology, an annual review 21: 455-531. Robineau, D., & J. Rose, 1983. Note sur le Stenella longirostris (Cetacea, Delphinidae) du golfe d’Aden. Mammalia, 47:237-245. Rudolph, P., Smeenk, C. & Leatherwood, S. 1997. Preliminary checklist of cetacea in the Indonesian Archipelago and adjacent waters. Zoologische Verhandelingen. Leiden, Nationaal naturhistorisch Museum. Rudolph, P. & Smeenk, C. 2002. Indo-West Pacific marine mammals. In: Perrin, W. F., B. Wursig & J. G. M. Thewissen (eds), Encyclopedia of marine mammals. Academic Press, London. Pp. 617-625. Van Waerebeek, K., Gallagher, M., Baldwin, R., Papastavrou, V. and Al-Lawati, S. M. 1999. Morphology and distribution of the spinner dolphin, Stenella longirostris, rough-toothed dolphin, Steno bredanensis and melon-headed whale, Peponocephala electra, from waters off the Sultanate of Oman. J. Cetacean Res. Manage 1: 167-177. Voris, H. K. 2000. Maps of Pleistocene sea levels in Southeast Asia: shorelines, river systems and time durations. Journal of Biogeography 27: 1153-1167. Weber, M., 1923. Die cetaceen der Siboga-Expedition. Vorkommen und fang der cetaceen im Indo-Australische Archipel. Siboga-Expeditie 58. E.J. Brill, Leiden. Pp. 1-38, Pls I-III.
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34 Abundance estimation of freshwater Irrawaddy dolphins
CHAPTER 4
Density and abundance of the Irrawaddy dolphin, Orcaella brevirostris in the Mahakam River of East Kalimantan, Indonesia: A comparison of survey techniques
The Raffles Bulletin of Zoology, Supplement 10, pp 85-95, 2002
The river was scanned on top of the research vessel at 3,5 m eye-height above the water surface by use of binoculars and naked eye in order to detect dolphins surfacing. One rear observer (not in this picture) checked for dolphins missed by the front observers.
35 Chapter 4
ABSTRACT
On-going monitoring surveys are being conducted on a freshwater Irrawaddy dolphin population, locally referred to as the Pesut, inhabiting the Mahakam River in East Kalimantan, Indonesia. The aim of the study is to provide detailed information on the abundance, distribution, and ecology relevant to conservation of this population. This paper describes results from surveys in February 1999 - July 2000 that relate to population abundance estimates and compares different survey techniques. The primary goal of these investigations is to develop a conservation program for effective management of Indonesia’s only freshwater dolphin population, which is considered to be critically endangered. In this study, both modified strip-transect and direct count survey-methods were employed. Total search effort in the Mahakam River amounted to 4260 km (397 hours). Results of eight sighting surveys indicate that the dolphins in the mainstream Mahakam range from 180 km above the mouth to 480 km upstream, seasonally inclusive of several tributaries and lakes. However, dolphins are reported to sporadically move as far down- and upstream as 80 km and 600 km, respectively. The distribution of the dolphins changes seasonally and is influenced by water levels and variation in prey availability. The middle Mahakam area (MMA) and tributaries between 180 km and 350 km upstream were identified as primary dolphin habitat, based on highest dolphin densities. Sighting rates calculated for medium water levels in the MMA in 1999 and 2000 are nearly similar (c. 0.09 dolphins/ km, CV=25%, 49%). Highest sighting rate for the MMA was recorded at low water levels (0.142 dolphins/ km, CV=51%), indicating that dolphins are congregating in the main river in deeper waters. Lowest sighting rate was recorded at high water levels (0.035 dolphins/ km, CV=33%), suggesting that dolphins have moved upstream into the tributaries. Total mean abundance-estimates, based on density estimates and direct counts, were both 34 dolphins. However, the mean estimate based on density estimates exhibited more variation (CV = 25%), than the mean direct count estimate with associated CV of 5%. Unless a modified density sampling technique has been developed that is appropriate to the river conditions and takes into account dolphins daily migrations between main river and tributaries, direct count studies seem a more useful tool for assessing abundance of this particular freshwater population.
36 Abundance estimation of freshwater Irrawaddy dolphins
RINGKASAN
Pada survei monitoring yang telah dilakukan pada populasi lumba-lumba Irrawaddy air tawar, masyarakat setempat menyebutnya Pesut, mendiami Sungai Mahakam di Kalimantan Timur, Indonesia. Tujuan dari penelitian adalah untuk menghasilkan informasi yang lengkap mengenai jumlah, penyebaran, dan ekologi berkaitan dengan perlindungan populasi pesut. Tulisan ini menjelaskan hasil survei dari Februari 1999 – Juli 2000 yang berhubungan dengan perkiraan jumlah populasi dan membandingkan teknik survei yang berbeda. Tujuan utama dari penelitian ini adalah untuk mengembangkan suatu program konservasi yang efektif demi pengelolaan satu- satunya populasi lumba-lumba air tawar di Indonesia, dimana dapat dianggap terancam kepunahan. Pada penelitian ini, metode yang digunakan adalah strip-transect dan survei penghitungan langsung. Total penelitian di Sungai Mahakam mencapai 4260 km (397 jam). Hasil dari delapan survei pengamatan menunjukkan bahwa pesut berada di jalur utama Mahakam berkisar antara 180 km sampai dengan 480 km ke arah hulu, berdasarkan musim juga termasuk beberapa anak sungai dan danau. Namun, lumba-lumba dilaporkan sesekali bergerak jauh ke hilir dan ke hulu sepanjang 80 km dan 600 km. Penyebaran lumba-lumba berubah sesuai musim dan dipengaruhi oleh ketinggian permukaan air dan ketersediaan makanan yang bervariasi. Di Daerah Tengah Mahakam (DTM) dan anak sungai antara 180 km dan 350 km ke hulu telah diidentifikasikan sebagai habitat utama lumba-lumba, didasarkan pada kerapatan tertinggi lumba-lumba. Penampakan dihitung rata-rata pada permukaan air sedang di DTM pada 1999 dan 2000 hampir sama (c. 0,09 lumba-lumba/km, CV = 25%, 49%). Angka pengamatan tertinggi untuk DTM dicatat pada level air rendah (0,142 pesut/ km, CV = 51%), menunjukkan bahwa lumba-lumba berkumpul pada jalur sungai utama di perairan yang lebih dalam. Penamp = 33%) menunjukkan bahwa lumba- lumba bergerak mudik ke dalam anak sungai. Taksiran tengah total jumlah didasarkan pada perkiraan kerapatan dan perhitungan langsung, keduanya menunjukkan 34 individu. Namun, perkiraan tengah di dasarkan pada taksiran kerapatan menunjukkan lebih banyak perbedaan (CV = 25%), dibandingkan dengan taksiran tengah dari penghitungan langsung dengan hasil CV 5%. Kecuali telah dibuat suatu perubahan teknik pengambilan contoh kerapatan, yang sesuai untuk kondisi sungai dan memasukan perhitungan perpindahan harian lumba-lumba antara sungai utama dan anak sungai, penelitian dengan penghitungan langsung tampaknya menjadi cara yang lebih berguna untuk memperkirakan banyaknya populasi lumba-lumba air tawar yang khusus ini.
INTRODUCTION
River dolphins and porpoises are among the world’s most threatened mammals. The habitats of these animals has been degraded by human activities, in some cases resulting in dramatic declines in their abundance and range (Reeves et al., 2000). In
37 Chapter 4
Indonesia, one facultative freshwater dolphin population of Orcaella brevirostris, or Irrawaddy dolphin (locally referred to as Pesut) inhabits the Mahakam River and associated lakes in East Kalimantan. The species is found in shallow, coastal waters of the tropical and subtropical Indo-Pacific and in the Mahakam, Ayeyarwady and Mekong river systems (Stacey & Arnold, 1999). The status of the Irrawaddy dolphin in the Mahakam River was changed from ‘Data Deficient’ to ‘Critically Endangered’ in the IUCN Red List of Threatened Animals in 2000 (Hilton-Taylor, 2000). The species is protected in Indonesia and has been adopted as a symbol of East Kalimantan. Preliminary investigations on population abundance were made from late February 1997 to early April 1997 (Kreb, 1999). Thereafter, the current research project was undertaken, which began in February 1999 and will continue at least until November 2001. This paper describes research on dolphin abundance and an evaluation of the methods employed during surveys in February 1999 to July 2000. Relatively few published studies exist on the Irawaddy dolphin population in the Mahakam River. Studies so far have focused on their distribution and daily movement patterns in Semayang-Melintang Lakes and, in the region connecting the Pela and Melintang tributaries (Priyono, 1994), and on bio-acoustics (Kamminga et al., 1983). Earlier reports on their abundance were given by the Indonesian Directorate General of Forest Protection and Nature Conservation, which reported the existence of a population of 100-150 individuals for Semayang Lake, Pela River, and adjacent Mahakam River (Hardjasasmita, 1978) and an estimate of 68 individuals by Priyono (1994). However, no methods were presented about how both estimates were derived and these estimates may be merely guesses. A preliminary survey conducted by the author together with the East Kalimantan Nature Conservation Department reported that encounter rates in the middle Mahakam segment were 0.06 dolphins per linear kilometre in 1997 (Kreb, 1999).
METHODS
Study area
The Mahakam River is one of the major river systems of Kalimantan and runs from 118o east to 113o west and between 1o north and 1o south (Figure 1). The climate is characterised by two different seasons, namely dry (from July-October, southeast monsoon) and wet season (November-June, northwest monsoon) (MacKinnon, 1997). However, dry and wet periods, alternate during the wet season as well. The Mahakam River is the main transport system in the central part of East-Kalimantan. The river measures about 800 km from its origin in the Müller Mountains to the river
38 Abundance estimation of freshwater Irrawaddy dolphins
39 Chapter 4
mouth. The Semayang and Melintang Lakes are 10,300 hectares and 8,900 hectares, respectively (MacKinnon et al., 1997). Average widths of the river in the upper segment (from Long Bagun to Muara Benangak), middle segment (Muara Benangak to Muara Kaman) and lower segment (Muara Kaman to Samarinda), are 160 m, 200 m and 390 m, respectively, determined from visual estimates (see Survey methods). Highest mean transparency measured in the main river at low water levels is 24 cm (range 10-35 cm). Mean depths in the upper, middle, and lower segments, and in Semayang and Melintang Lakes were 10 m, 15 m, 12 m, 1.1 m and 1.3 m respectively. Differences in the water levels of the main river between high and low water conditions range as much as 10 m in ‘normal years’ (during extreme drought a maximum difference of 20 m may be recorded), whereas the maximum difference in lakes is c. 5 m. Water levels rise vertically and only slightly horizontally. Large passenger boats are able to navigate up to Long Iram (c. 427 km upstream). These boats of maximum 800 hp are only able to move as far upstream as Long Bagun (c. 560 km upstream) at high water levels. Rapids begin upstream of Long Bagun, which are only navigable by large motorised canoes (minimum 40 hp). These rapids limit dolphins from ranging further upstream. Coal mining, gold digging and logging activities pollute waters throughout the Mahakam. Fisheries in the middle segment of the Mahakam River and Semayang, Melintang, and Jempang Lakes are intensive, with an annual catch of 25,000 to 35,000 metric tons since 1970 (MacKinnon et al., 1997).
Field methods
Survey area Three surveys covering the entire study area were conducted in 1999 at low, medium and high water levels and one survey at medium water levels in 2000. Each one took about 4 weeks. Survey coverage included Ratah, Kedang Pahu, Belayan, Kedang Kepala, Kedang Rantau tributaries, Semayang and Melintang Lakes, as well as connecting tributaries, Pela and Jempang, part of the delta area, and minor tributaries (Figure 1). It was not possible to survey representative transects and extrapolate, because of the unpredictable variation of dolphin densities. Therefore, the entire range of dolphins in the Mahakam was surveyed. Ranges for different seasons were identified during preliminary surveys and from interviewing fishermen about the dolphins’ occurrence and their prey. To study the relation between fish- and dolphin migrations, interviews were held at different locations along the river to identify seasonal fish abundance for 25 species, including those suspected or known to be preyed upon by dolphins. Generally, dolphins did not frequent upstream areas of tributaries, where there was no more connection with freshwater swamp lakes that replenish the river with fish. If during the survey, the water conditions were such that
40 Abundance estimation of freshwater Irrawaddy dolphins
no dolphins were expected to occur in a particular area of a tributary and interviews with fishermen confirmed their absence for that period, the area was not surveyed. Water conditions in upstream areas of some tributaries connected with freshwater swamp-lake habitat, which did not favour dolphin occurrence during particular seasons were flooding, heavy currents in combination with lots of floating tree trunks, aquatic weeds and a high acidity. Also, decreasing water levels caused the dolphins to move downstream in the tributaries together with their prey. During one of the four intensive surveys conducted in May/ June 2001 at medium, decreasing water levels, areas that didn’t seem likely to be visited by the dolphins at that particular water level condition were nevertheless visited to check if this was true. Indeed no dolphins were found in these areas, which represented upstream areas of particular tributaries. Seventeen transect lines were surveyed in different habitats. Table 1 presents only those transects on which at least one sighting was made during one or more seasons. Each transect could be finished within one day. Eight transects were in the main river (c. 66 km), two were in the lakes (c. 48 km), five were in four middle segment tributaries (c. 50 km), and two were in upper segment tributaries (c. 32 km). In addition to transects, narrow tributaries that become accessible during high water levels for boats and potentially for dolphins were also surveyed.
Survey methods Modified strip-transect surveys were conducted, using the width of the river as the strip width for each transect within the identified dolphin distribution area. Modification thus included that strip width was not calculated as a function of perpendicular sighting distance because this distance was not a function of detection probability but of dolphins preferred distribution along the width of the river due to restrictions imposed by river width (see Results, Detection probability). Line-transect surveys were only conducted in Semayang and Melintang Lakes. Parallel line-transects were spaced at 1.5 km apart. Transect lines in the lakes were systematically designed to cover the entire survey area and no prior assumptions were made regarding dolphin distribution. Within the dolphin distribution area, the vessel always travelled in the central part of the river, even in river bends, which was possible because the main river was deep enough to do so. Only in areas where width of river was less than 100m, such as in some tributaries, was the boatsman free to travel near the riverbank. The widest arms of the delta area (width = >400 m) were surveyed following a zigzag pattern. Various environmental random samples, such as depth, clarity, pH and surface flow rate were taken on average five times a day at 3-5 spots along the width of the river, but only depth and clarity samples were analysed at the time of writing and presented in the survey area text. Depth was measured by lowering a rope with attached weight and markings every meter to the bottom of the river. Transparency was measured using a Secchi disk. When taking the depth and clarity measurements, the boat would drift with the flow so that the rope would be hanging in a straight line.
41 Chapter 4
The river was scanned from an elevated platform (eye-height c. 3 m above water level) on top of a motorised boat (12 hp) moving at a speed of c. 10 km/ hr in the central part of the river, covering an average distance of 50 km per day. The observation team consisted of at three observers, who rotated at 30-minute intervals. The first observer scanned the river continuously with 7x50 binoculars. The second observer searched for dolphins with naked eyes and recorded search effort and geographical data every 15 minutes by aid of a GPS. At the same time, environmental data were recorded, such as rain, wind, sun glare, fog conditions, cloud coverage and the extent to which floating tree logs and water weeds impaired sighting ability. Survey effort was suspended when sighting conditions were such that they impaired sighting efficiency, due to heavy rainfall and fog. Sun glare was never so bad that survey effort had to be ended and was anticipated by using a good binocular, head protection and sunglasses. The front observers alternated scanning with binoculars every 15 minutes to keep concentration high. During the first survey, a rear observer was present during the entire survey in primary dolphin habitat. All dolphins that were sighted by this observer involved groups that were located in or just after a river bend. Therefore, during the next surveys a rear observer was only present during and after river bends and confluence areas to allow the third observer at the rear to regain concentration for the next turn at the front observers’ position. Upon sighting dolphins, linear sighting distance and position of the first sighted dolphin along the width of the river was recorded (for calculation of relative perpendicular sighting distances). Dolphin positions were recorded in one of the following three categories. The central part was defined as the nearest area on each side of the transect line that occupies 25% of half the river width. On each side of the transect line, the area in between centre and shore occupied 50% of half the river width. The shore area was defined as an area of 25% on each side of the transect line nearest to the shore. Distance to the dolphins was estimated visually by the observer. A bridge of known distance that crossed the river in Samarinda, was taken as a reference for further distance estimations. During the survey, each fifteen minutes, the river width was estimated and agreed upon by all observers, so that distance estimations became more standardised. In addition, observers now and then referred to floating objects in the river and tried to standardise their estimation. During sightings, for between one half-hour and one hour, dolphins were counted, identified and their group composition was recorded (see Group size and sighting definition). The upper picture in Figure 2 (a) portrays two adults and one calf in the centre. Because of the group’s tight formation calves may easily remain undetected. Therefore observation time was rather long to allow for most accurate group size estimation. By aid of binoculars and naked eye alone observers tried to look for identifiable marks on the dolphin’s body and dorsal fins and drawings were made of the marks. Also, photographs and video footage were taken for identifying individual dolphins, but these analyses are not yet complete. The picture in the centre of Figure 2 (b) shows a typical slow surfacing pattern, which enables observers to notice and
42 Abundance estimation of freshwater Irrawaddy dolphins
Figure 2a. Two adults and one calf in the center swimming in tight formation
Figure 2b. Typical slow surfacing pattern enabling the observers to take notice of natural markings on the dolphin’s body and dorsal fin by aid of the naked eye and binoculars.
Figure 2c. A dolphin surfacing after a deep dive, producing a loud blow. Also, during a ‘normal’ dive- and surfacing pattern, the dolphins regularly produce blows, facilitating detection.
43 Chapter 4
photograph natural markings on the dolphin’s body. General and individual behaviours were recorded in combination with group- dive and surfacing times. Group diving times were collected during 14 sightings and were recorded for c. 30 minutes from the start of a dolphin’s dive and the surfacing of the next dolphin. However, time gaps of less than 3 seconds were ignored to reduce a bias towards short dive time intervals and were included in the duration of group-surfacing, i.e. the time a group is available on the surface for observation. The picture below in Figure 2 (c) shows a dolphin surfacing after a deep dive, producing a loud blow. Also during a ‘normal’ dive and surfacing pattern, the dolphins regularly produce blows, facilitating detection. Finally after all observations were made, the same kinds of samples were taken as those during search effort.
Double counting By the aid of identification of individual dolphins, I attempted to prevent double counting of dolphins on the same transects. Additionally, for the direct count analysis, I tried to reduce double counting of the same group or subgroup (in the case of an aggregation of dolphin groups) encountered on different transects. The following assumptions were made when determining if groups were similar: 1) minimally one individual of the (sub) group was re- identified. 2) similar age-classes. 3) similar (sub) group sizes, i.e., within the range of minimum and maximum group size estimates, as the earlier encountered group. 4) time elapsed between both encounters and distance between both locations should be in accordance with dolphins’ movements (mean speed is < 6 km/ hr). 5) absence or presence of dolphins that are easily recognisable by naked eye in only one of both groups did not favour similarity. 6) in case of any uncertainty, a non-conservative approach was preferred and groups were considered to be different. Preliminary analysis of studies of dolphins that were followed in one confluence area during three periods for on average six consecutive days, revealed that group composition during these days was relatively stable. That is to say, close interactions among different groups never exceeded one hour, which is the time that is spent observing the dolphins during surveys, which aim to identify total abundance of the population. Opposite to the problem of double counting is the problem of dolphins that moved in one direction at night whereas the survey team would move in the other direction and thus miss a sighting. However, replicates of surveys may account for this problem.
Group size and sighting definition For the calculation of sighting rates, mean group sizes are multiplied by number of sightings and divided per linear kilometre of river surveyed. To this aim it is necessary to determine what constitutes a sighting or group. Within this study, dolphins that are leaving the initial observed group of dolphins, i.e. moving outside the visibility of the
44 Abundance estimation of freshwater Irrawaddy dolphins
observers (c. 400 m), which remain close to the initially sighted group, during the observation period (on average one hour), are considered to belong to another group and constitute a new sighting. On the other hand, new dolphins that join the initial group are included in the group size estimate unless they move away from the initially sighted group within the observation period. Although for the new group no sighting distance data are available, the approach of defining group size as described above is preferred for the density and abundance estimates because the chance of a sighting of a group, whose composition remains the same during the observation period, is higher than the chance of encountering an opportunistic aggregation of different dolphin groups. The decision to separate dolphin groups because of their non- or short- duration interaction also makes comparisons of mean group sizes and number of sightings more meaningful among different surveys. Of the 58 sightings and groups of dolphins in total that were used to calculate the abundance and density estimates presented here, three sightings involved dependent sightings of groups that only interacted for a brief time during the observation period. Therefore, they were treated as three different sightings. The following example is given to elucidate what constitutes a dependent sighting: After an initial sighting was made of 3 individuals, which were followed downstream, another group of 9 dolphins was encountered. However, the initial group of 3 dolphins moved downstream away from the new group. While continuing observation on the group of 9 dolphins, another group of 3 dolphins from upstream joined the group for a moment and then moved into a small tributary, whereas the group of 9 dolphins moved upstream. So, instead of considering this as one sighting with 15 dolphins, I consider this as 3 different sightings and groups. The size of the group upon initial sighting includes all dolphins visible to the observers using a best, minimum and maximum estimate. Final decision about the group size estimation was taken by the primary researcher. In most cases at least one- half hour was needed to get a good count (depending on the group size), carefully looking for natural markings to identify individuals and determine if two surfacings were made by the same dolphin.
Availability bias and perception bias To account for undetected dolphins due to the dolphins’ submergence within the observers’ visibility field (availability bias) and reducing observers’ perception bias (those dolphins that surface in the visual range, but are still missed by all observers), a rear observer was present (see Survey methods). An attempt was made to reduce perception bias by suspending survey effort when sighting conditions were such that they impaired sighting efficiency, due to heavy rainfall and fog. Sun glare was anticipated by using a good binocular, head protection and sunglasses. Finally, scanning bouts with binoculars were rather short, i.e. 15 minutes, to keep concentration high. For comparison of increased sighting efficiency, two additional seasonal surveys (besides the four seasonal surveys described in this paper) of higher
45 Chapter 4
observer’ intensity were conducted. Each of these surveys covered the same transects in primary dolphin habitat and one observer was added to the observer team that now consisted of 4 observers (two front observers, one rear observer and one observer stand-by).
Analysis
Mean sighting frequencies were calculated per transect, habitat segment and water level condition. Mean number of sightings and sighting rates were calculated as the mean number of sightings and sighting rates of upstream and downstream surveys per transect and water level condition. Except for one segment representing a line transect in a lake, all transects were replicated per water level condition. For the lake transect that was only surveyed once, the number of sightings recorded were taken as the mean in order to be comparable with the other mean number of sightings, assuming that a replicate survey in the same period conducted in this lake would yield the same results. For the calculation of mean dolphin densities, the mean river width per segment was taken as the mean strip width. Abundance estimates were calculated for each transect as a product of dolphin densities and total transect area completed. Estimates per transect were summed to get total abundance per water level condition. To check for the variation in abundance estimates derived from different surveys, the coefficient of variation was calculated directly from the variance of each seasonal estimate in relation to their mean. Because of the assumption that all groups within the strip width would be detected by either front or rear observers (see Analysis, Detection probability), the fact that there was no group size bias detected, and the entire possible range of dolphins was covered for each survey (except for high water levels), no other components were included in the calculation of CV. Although a considerable variation in group-size was found among different surveys, this is more likely to reflect a biological variation than a size bias related to detection probability. Therefore, instead of calculating the variance of numbers of sightings and group sizes, the CV was directly applied to the abundance estimates. The estimates of the high water level survey were excluded because several transects were not completed. In addition, CVs were calculated per habitat segment, i.e. for the middle-river segment and two tributaries per water level condition to check for the variation of sighting rates among different transects (see formula below). Of the other habitat segments only one transect was completed per water level condition and these segments represented secondary habitat, in which only during specific seasons dolphins were sighted. Therefore, no CVs for seasonal abundance estimate were calculated, but the CV for the middle- river segment may be used as an indication of seasonal variation. Lastly, CVs were calculated for different river segments for the mean abundance estimates of surveys that were both conducted at medium water levels in 1999 and 2000:
46 Abundance estimation of freshwater Irrawaddy dolphins
= g.n R i L
= R i Di Wi
N = ∑ (Di. Ai)
(r − R )2 S (R ) = ∑ j i i − (x j 1)
S.100 CV = R i
Where Ri = mean sighting rate per river segment; r j = mean sighting rate per transect
i = river segment; j = transect
n = number of sightings; L = length of transect completed
D = mean dolphin density; W = mean strip width
N = total abundance within survey area; A = total transect area
S = standard deviation; xj = number of transects completed
CV = coefficient of variation
47 Chapter 4
All sightings are included in the analysis of sighting rates, density- and abundance estimates based on density sampling techniques, except for double counts within one transect and off effort sightings. For direct counts, double sightings on different transects per one-way survey were excluded. In case uncertainty existed about whether two groups consisted of the same dolphins, a non-conservative approach was chosen and these numbers were added in total count. The sightings made by the rear observer are included in total abundance estimate calculations of both survey methods. The percentage of sightings made by front and rear observers are presented in Table 2. Sightings made in one tributary of the upper river segment involved one group of 5 dolphins whose movements were restricted in an area of c. 1 km by two rapids. Sightings made during medium- and high water levels in 1999 are off-effort sightings by other persons than the survey team. The survey team was not able to move upstream of the rapids because of heavy currents due to recent rainfall. However, according to different people in this area, the dolphins have moved upstream of the rapids since October 1998 during a big flood. Because of the overall low sample size these sightings are included in the abundance estimates and because they were confirmed during the next surveys. Correction factors to account for undetected dolphins have been left out because there is a lack of a detailed dive time study. Therefore, it is tentatively assumed that all dolphins will be sighted by front or rear observers within the primary dolphin habitat (middle river-segment, mean width = 200 m, SD = 54), upper river segment (mean width = 161 m, SD = 48), and tributaries (max width of 150 m). Because linear sighting distances only start decreasing after 400 m with 100%, and the survey boat always travelled in the central part of the river, these sighting distances are within the above-mentioned width ranges (see Results). Linear sighting distances of rear sightings and of sightings made in narrow tributaries with many river bends where the average distance between two bends < 400 m were excluded from analysis. Sighting distances of dolphins in river bends are most likely to be restricted as maximal sighting distance is dependent on the distance of two river bends, whereas the sighting distances made by the rear observer may be influenced by the boat’s engine while passing by.
Detection probability Sighting probability was investigated for the following variables: 1) Firstly, linear sighting distances were plotted against the number of sightings made (Figure 3) and tested with chi-squared statistics to investigate if there are significant differences in detection probability of dolphins within the strip width. 2) Relative perpendicular sighting distances were expressed in percentages over three categories in relation to the number of sightings. 3) In addition, the correlation between linear sighting distances and group sizes was investigated and the correlation was measured with the
48 Abundance estimation of freshwater Irrawaddy dolphins
coefficient of determination (r2) (Figure 4). 4) Group dive times were plotted against group size and the Spearman Rank correlation coefficient (rs) was calculated (Figure 5). I preferred to calculate relative perpendicular sighting distances (PSD) because of biases related to the calculation of absolute PSD such as variation in river width between different river segments, and the fact that the vessel cannot maintain a straight course in river bends, leading to biases in calculation of PSDs, whereas many sightings are associated with river bends. In addition, the dolphins restricted and preferred distribution along the width of the river causes both relative and absolute PSD to be of little value to define strip widths as they do not reflect observers’ sighting abilities. Therefore, I did not calculate the probability density function at zero perpendicular distance f(0).
RESULTS Density and abundance estimates
Total search effort in the Mahakam River amounted to 4260 km (397 hours). Actual sightings in the main river segment were confined between Muara Kaman (c.180 km upstream) and Muara Benangak (c.375 km upstream) including tributary Belayan (1 km upstream), tributary Kedang Pahu (max. 80 km upstream), tributary Ratah (480 km upstream main river and 20 km upstream the tributary past a rapid) lake effluent Pela and Lake Semayang (Figure 1). However, depending on water level conditions, the dolphins may move as far downstream in the main river until Loa Kulu (80 km upstream of mouth), whereas their uppermost distribution is limited by the high rapids past Long Bagun (560 km upstream of mouth). Sighting rates for each transect and river segment in which dolphins were sighted are in Table 1. Dolphins were sighted in 6 different habitat segments: middle-river segment (MR, mean width = 200 m, SD = 54); narrow middle-river tributary connected with confluence area with highest dolphin densities (MRT1.1, mean width = 43 m, SD = 13); middle-river tributary in swamp lake area (MRT2.1, mean width = 81m, SD = 13); very narrow upper segment (MRT1.2, mean width = 34 m, SD = 14) of the middle river tributary (MRT1.1), which falls dry in dry season; upper-river tributary with rapids and rock bottom substrate (URT1, mean width = 75 m, SD = 11); Lake Semayang, surrounded by freshwater swamp forest habitat (LS). Mean sighting rates for medium water levels in 1999 and 2000 are nearly similar in the MR segment (0.092 dolphins/ km and 0.096 dolphins/ km with CVs of 25% and 49%). The maximum mean sighting rate for the MR segment was recorded at low water levels (0.142 dolphins/ km, CV = 33%), whereas lowest mean sighting rate in this segment was recorded at high water levels (0.035 dolphins/ km, CV = 51%), indicating that dolphins have moved upstream in the tributaries. Also, the dolphins’ seasonal movements followed changing water levels and seasonal variations in prey availability.
49 Chapter 4 i N
42.7 2000
1.2 i mean D 35 - - 0.48 19.9 0.20 2.9 0.61 8.6 0.61 8.6 5.23 17.1 0 0 0 0 2.29 5.7 49%
i mean R
- 0.096 0.041 0.123 0.123 0.225 0 0 0.172
mean g = 5.7 dolphins MEDIUM WATER LEVELS mean n area; # = no density calculated i N
’99
i mean D 34.7 7.5 34.7 32 - - - 0.71 26.6 3.5 0.71 26.6 0.55 7.6 0.5 0.83 11.4 1.5 0.76 7.6 1.5 0 0 3 - - 0 1.03 3.8 0 1.6 3.8 1 33% 33% = Muara Pahu – Muara Lawa; MRT 1.1
i mean R
- 0.142 0.110 0.165 0.152 0 - 0.084 0.12
MRT
mean g = 3.8 dolphins LOW WATER LEVELS LOW WATER mean n = Ratah tributary = Muara Ratah – rapids; LS = Lake 1 i
N ’99
i mea n D # 2.6 - 14.3 9 14.3 18 0.18 6.5 7 0.19 2.6 2 0.09 1.3 3 0.26 2.6 2 0 0 0 2.5 2.6 - - - 1 1.1 2.6 1 51% 51% where dolphins were sighted. This table only presents those ng was made. Each transect was replicated for each water level = Kedang Pahu tributary;
i 50 mean R 1.1, 1.2 mea n n HIGH WATER LEVELS mean g = 2.6 dolphins 1 0.05 5.5 2.5 0.035 1 0.038 0.5 0.019 1 0.052 0 0 1 0.086 - - 1 0.08
= mean sighting rate; D = mean density; N = total abundance; ; g = average group size
i represent the means of the replicated surveys. N 0 25.5 34 19.2 6.4 4.8 8 3.2 - 0 3.2 25% ’99
i mean D
i mean R 0 0 0.092 0.2 0.092 0.46 0.069 0.34 0.115 0.46 0.042 0.98 - - 0 0 0.1 1.3 mean strip width; L = transect length; - = no data available because of non-surveyed mean g = 3.2 dolphins mean n MEDIUM WATER LEVELS 0 6 2 1.5 2.5 1 - 0 1 = Belayan tributary = Muara Belayan until Tuana Tuha; URT 2.1 ) Km L ( 52 207 69 69 69 76 30 45 33 ) Km 0.200 0.200 0.200 0.200 0.043 0.034 0.081 0.075 mean W (
/ ) ) (MR) 1.1 1.2 2.1 1 1,2,3 1 2 3 condition and number of sightings in this table transects on which during one or more season at least one sighti WATER LEVEL . Sighting rates, density and abundance estimates for each transect TRANSECT N (count) MR MR MR MR MRT MRT MRT 8 (strip) URT (count) LS - N CV(R N = middle river segment = Muara Kaman – Muara Benangak; MRT
1,2,3
River Main Tributary Lake HABITAT because of unknown strip width; CV = coefficient of variation. per water level; i = habitat stratum; W = Semayang; n = mean number of sightings per replicated transect ; R Chapter 4 Table 1 MR =Muara Lawa – Nyawatan; MRT
Abundance estimation of freshwater Irrawaddy dolphins
Mean sighting rate and mean abundance of the combined medium water level surveys is 0.09 dolphins/ km and 19 dolphins (CV = 35%) in the entire MR segment and 0.134 dolphins/ km and 10 dolphins (CV = 97%) in the MRT1.1 segment. No significant differences in mean abundance of dolphins were found between the average abundance of dolphins per transect in the MR segment (mean width = 200 m) and the transect in the MRT1.1 segment (mean width = 43 m) (χ2 = 0.77, d.f. = 1, P > 0.05). Mean abundance in the URT1.1 segment at medium water levels is 4 dolphins (CV = 40%). Total mean abundance estimate of three completed (medium water levels 1999 and 2000 and low water level 1999) and replicated (up-and downstream) surveys based on density estimates (calculated from strip-transects) and direct counts are both 34 dolphins (with respective CVs of 25% and 5%). Mean group sizes of dolphins observed at medium, high and low water levels in 1999 and medium water levels in 2000 are 3.2 dolphins (median = 3; range = 1-7; SD = 2.1), 2.6 dolphins (median = 1; range = 1-6; SD = 2.3), 3.8 dolphins (median = 3; range = 1-8; SD = 2.3) and 5.7 dolphins (median = 5; range = 3-10; SD = 2.4) respectively.
Detection probability
When calculating the percentages of initial sightings in relation to relative perpendicular sighting distances (position along the width of the river), I found that the number of initial sightings peaked near the shore (45% of total n = 49), but not significantly (χ2 = 2.9, df = 2, P>0.05). The remaining sightings were nearly equally spread over the two other segments, i.e. the centre area of the river (29%) and the area in between centre and shore (26%). On the other hand, the number of sightings (total n = 33) were found to decrease sharply with 100% only after 400m linear sighting distance (Figure 3). No significant variation was found among the sighting distances inside of 400 m (χ2 =5.3, df = 5, P > 0.05). Because the maximum mean river width for one of the transects (MR1) within dolphin distribution area is 238 m (range = 120 m – 400 m, SD = 62 m), there is no apparent bias towards undetected dolphins near the shore, because maximum sighting distances are greater than one-half the survey strip. Therefore, I assumed that the probability of sighting dolphins was uniform throughout the survey trip. Because I found no distinct decrease of sightings in relation to perpendicular sighting distances, linear sighting distances (n = 35) were plotted against group size to see if there is any detection bias for any group size (Figure 4). No significant correlation was found between the two variables (r = 0.132, df = 33, P > 0.05) and only 1.7 % of the variation in group-sizes is accounted for by variation in linear sighting distances (r2 = 0.017). Dolphin group dive data were collected only during 14 sightings. However, results presented in Figure 5 seem to indicate that group dive times are negatively related with group size, i.e. small groups have longer mean group dives per sighting
51 Chapter 4
Detection probability 10
8
6
4
2 No. of sightings
0 10 88 166 244 322 More Linear sighting distances (m)
Figure 3. Histogram showing the frequency of sightings per linear sighting distance category.
Group size bias 500 lin.sight.dist 400 Predicted lin.sight.dist 300
distance 200
Linear sighting 100
0 0246810 Group size
Figure 4. Scatter plot of linear sighting distances and group size indicating probability of any detection bias related to group size.
than large groups (rs = 0.665; P < 0.01; n = 14). Mean of all average group dive times per sighting is 72.0 sec (median = 38.3; SD = 69.2; range = 5-240). Mean time that a group of dolphins is visible per surfacing (time between first dolphin’s surfacing and last dolphin’s diving allowing for maximum interval of 3 sec.) is only 2.5 seconds (2-6 sec). Although a lower detection probability is expected for dolphins with a small group size due to longer dive times, no detection bias was found for any given group size in relation to sighting distance as stated earlier (Figure 4). Additionally, single dolphins were frequently observed: 29% of all on effort sightings (n = 49) constitute single dolphins.
52 Abundance estimation of freshwater Irrawaddy dolphins
Group Dive Times and Group Size 300 250 200 150 100 50 Mean dive time (sec.) 0 02468 Group size
Figure 5. Scatter plot showing a negative relation between group size and mean group dive times.
The percentage of sightings during the four surveys covering the entire dolphin distribution range, made by an observer at the front of the boat using binoculars was on average 63 % and that by a front observer without binocular was 31% (total n = 52). On average, during each survey 6 % of all sightings were missed by the front observers, being observed only by the rear observer (Table 2). During two additional one-way surveys at medium to decreasing water levels conducted in the middle-river segment (MR) whereby three transects were completed, observer efficiency was increased from three to four observers (data not presented in table). During each of these surveys, three sightings were made, all by the front observers.
Table 2. Observer perception bias (% sightings made per observer category); n = number of sightings
OBSERVER/ n FRONT FRONT REAR SURVEY PERIOD OBSERVER OBSERVER OBSERVER + BINOCULAR -BINOCULAR Surveys Feb/ March ‘99 14 50 % 36 % 14 % Surveys May ‘99 8 50 % 38 % 12 % Survey Oct ‘99 15 77 % 23 % 0 % Survey May/June 2000 15 75 % 25 % 0 % Total / Average 52 63% 31% 6 %
DISCUSSION
Two different methods, strip-transects and direct counts, were employed to estimate abundance for the Mahakam dolphin population. In this study, a modified form of strip-transect surveys was used. Instead of determining the effective strip width based
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on perpendicular sighting distances, the average entire river width was estimated per segment and used as strip width for density calculation. Two things were evident: 1) Dolphin positions along the width of the river at initial sighting peaked near the shore, (although not significantly) and 2) Linear sighting distances start decreasing slightly after 166 m and number of sightings made at 400 m linear distance have not yet dropped to half the number of sightings at 166 m (62%), but dropped to zero beyond 400 m. Because the maximum river width in the dolphin distribution area is 400 m (with strip width as follows 200 m), it seems reasonable to assume that sighting detection probability is not limited by strip width, but is more likely to be influenced by dolphin availability bias and observer perception bias. Also, river width in the Mahakam does not change much throughout seasons and floods almost only vertically instead of horizontally, in contrast to rivers like the Amazon. Sighting distances and river width estimations are visually estimated and are therefore likely to be biased. However, attempts were made to make distance estimations more standardised among the observers of the survey team and among different survey teams (see Survey methods). When comparing total abundance estimates that are calculated on the basis of density estimates calculated from strip-transects and those estimates based on direct counts, I found that the latter analysis method produced more consistent results for the three completed surveys (medium water levels in 1999 and 2000 and low water levels in 1999). Total mean abundance-estimates, based on density estimates and direct counts, were both 34 dolphins. However, the mean estimate based on density estimates exhibited more variation (CV of 25%), than the mean direct count estimate with associated CV of 5%. The higher variation among abundance estimates based on density estimates may arise from the fact that the abundance estimates for different segments, i.e., main river and tributaries, were added together to derive total abundance, whereas dolphins daily migrate between these areas. This problem does not exist for direct count estimates as these daily migrations are taken into account and double counts avoided (see Survey methods). No CVs of total abundance estimates per season were calculated because of the fact that segments other than middle-river segment consisted only of one transect. However, a seasonal CV for abundance was given in the middle-river segment for three completed transects. The highest sighting rate for the middle- river segment (0.142 dolphins/ km) was recorded at low water levels, indicating that dolphins are congregating in deeper waters of the main river. The lowest sighting rate (0.035 dolphins/ km) was recorded at high water levels, indicating that dolphins have moved upstream and into the tributaries. This movement pattern was also confirmed through interviews with local fishermen and coincides with fish-migration at first flooding. At high water levels, only two sightings were recorded in tributaries. However, this is probably not a representative figure, because three other middle-segment tributaries and the narrow upstream areas beyond tributary 1.2 (Kedang Pahu) were not surveyed. During the low water survey no dolphins were found to occur in the upper river segment,
54 Abundance estimation of freshwater Irrawaddy dolphins
although during a prolonged dry season (more than 3 months) dolphins are said to move to the upper river segment as far as Long Bagun (560 km upstream), as currents are less strong than during the other water conditions in this segment. However, the absence of observations in the upper river segment is not representative of the dry season’s low water levels, because of the short duration of the dry season. Also water levels had for a week increased rapidly in the upper segment, due to heavy rainfall. However, data were not included in the high water level category, as this category became of a prolonged period of high water levels and did not extend to the other river segments. The highest sighting rate recorded during low water levels for the middle Mahakam segment (0.14 dolphins/ km), is similar to sighting rates recorded for Irrawaddy dolphins in a segment of the Ayeyarwady River between Bhamo and Mandalay (0.16 dolphins/ km) (Smith & Hobbs, this volume). Average sighting rates during medium water levels in 1999 and 2000 were 0.09 dolphins/ km and similar to encounter rates recorded during a preliminary survey in 1997 in the same river segment and season (0.06 dolphins/ km) (Kreb, 1999). Compared to other freshwater dolphin species, rates are much lower than those recorded for Inia geoffrensis and Sotalia fluviatilis in segments of main channel of Amazon River (0.43 – 0.60 and 0.41 dolphins/ km, respectively) (Vidal et al., 1997; Martin & da Silva, 2000), and those recorded for Platanista gangetica, varying from 0.2 – 1.36 dolphins/ km (Smith, 2000; Smith et al., 2001). Total abundance estimates in this study of 35-42 dolphins are of the same order of magnitude as those for Lipotes vexillifer, of which the ‘best guess’ of current population size is a few tens of animals (Reeves et al., 2000). No significant differences were found between the mean abundance of dolphins at medium water levels (when there are no seasonal dolphin migrations) in two different transects (main river and tributary) within the primary dolphin habitat of different mean width (200 m and 43 m) (χ2 =0.77, d.f. = 1, P > 0.05). However, when comparing densities, a conclusion may be drawn for example that dolphin densities are higher in a narrow river segment than in a wider river segment, whereas sighting rates and abundance are nearly similar in the two segments. For that reason these densities should not be used for comparison between different river segments or with other studies. Instead, sighting rates and direct counts give a much more useful comparison. The following data are in favour of the reliability of the abundance estimates presented here: 1) The dolphin availability bias and observer perception bias seem low, and missed sightings by the front observers are partially anticipated for by using a rear observer. Moreover, in spite of a lower detection probability of dolphins with a small group size due to longer dive times, single dolphins were frequently observed (29% of all on effort sightings (n = 49) constitute single dolphins). In addition, no correlation was found between group size and linear sighting distance and number of sightings only drop sharply beyond 400 m. 2) There seems to be no bias towards undetected dolphins near the shore because most sightings (78%) were made at linear
55 Chapter 4
sighting distances (≥ 166 m) that cover the distance from centre to shore in primary dolphin habitat (mean distance is 200 m). In addition, initial dolphin sightings even peaked near the shore. 3) There is a high similarity of direct count abundance estimates during different surveys (CV =5%). However, with regard to direct counts a potential bias exists with regard to the estimation of best group size estimates. For this reason, absolute counts in the true sense of the word are not possible. The low number of observers may cause an underestimation of numbers and the fact that rear observers were only present in and after river bends and confluence areas, assuming that most dolphins in straight river stretches would be sighted by the front observers. On the other hand, the detection probability analyses plus the two repeated surveys in 2000 and 2001 with increased numbers of observers in the middle river segment suggest that this factor is not likely to influence the estimates significantly. However, the number of sightings was low during these last surveys as only three transects were covered and not the entire river stretch. So, the surveys with an added observer cannot really be compared in terms of the percentage of sightings that are missed by front observers and observed by rear observer due to unequal sample size. Recommendations for future studies are to conduct at least a yearly extensive and intensive monitoring survey during the dry season, covering the entire dolphin distribution range with a standard number of observers, i.e., two front observers, one rear observer and one observer at rest for 30 minutes in between 1,5 hours observing bouts. Photo-identification may also be a valuable tool to determine total abundance. Unfortunately, data collection and analyses are not yet complete at time of writing. Also, a detailed dive time study is required to address the dolphin availability bias more properly and the need to include a correction factor. In conclusion, I would say that for assessing abundance of the dolphin population in the Mahakam, both density- sampling techniques and direct-counts seem appropriate and yield numbers of the same order of magnitude. Nevertheless, the direct counts of different surveys exhibit less variation. A simple direct count also was suggested as the most appropriate method for assessing populations of obligate river dolphins (Smith & Reeves, 2000). However, recommendations for future studies in the Mahakam also include to develop a modified density sampling technique that is appropriate to the river conditions and takes into account the dolphins daily movements between the main river and tributaries.
ACKNOWLEDGEMENTS
I am grateful for the financial support that enabled this long term project to continue and also allowed me to participate in congress meetings to exchange and receive viable information and input. For this support I would first like to thank Ocean Park Conservation Foundation Hong Kong; Martina de Beukelaar Stichting; Stichting J.C. van der Hucht Fonds; Amsterdamse Universiteits Vereniging; Netherlands Program
56 Abundance estimation of freshwater Irrawaddy dolphins
International Nature Management (PIN/ KNIP) of Ministry of Agriculture, Nature Management and Fisheries; Gibbon Foundation; Stichting Fonds Doctor Catharine van Tussenbroek; World Wildlife Fund For Nature (Netherlands, US). I am also grateful to the following non-financial sponsoring institutions: Lembaga Ilmu Pengetahuan Indonesia (Indonesian Institute of Sciences), Balai Konservasi Sumber Daya Alam Kal-Tim (East Kalimantan nature conservation authorities), Directorate Jenderal Perlingdungan Konservasi Alam (General Directorate of Protection and Conservation of Nature), University of Amsterdam, Zoological Museum of Amsterdam, Universitas Mulawarman Samarinda. My special thanks goes to my assistants for their enthusiasm and great efforts during the fieldwork in the Mahakam: Hardy, M. Syafrudin, A. Chaironi, Zainuddin, Arman, M. Syoim, Budiono, Bambang, Sonaji, Syahrani, K.R. Damayanti, Marzuki and Yusri. In addition, I would like to thank the following persons in particular: P. J.H. van Bree, F. R. Schram, A. Arrifien Bratawinata, A. M. Rachmat, Padmo Wiyoso, I. Syarief, S., V. Nijman, A.Ø. Mooers, G. Fredrikson, T. Prins, T. Dunselman, I. Beasley, R.R. Reeves, all boatsmen, fishermen, villagers and colleagues that shared their information, and all those who showed their support in the project. Finally, I would like to thank B. Würsig, P. Rudolph, B.D Smith and T.A. Jefferson for their rigorous and helpful review of earlier versions of this manuscript.
REFERENCES
Hardjasasmita, H.A. 1978. Studi pembinaan habitat dan populasi pesut. Direktorat Perlindungan dan Pengawetan Alam, Bogor. Hilton-Taylor, C. 2000. 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, U.K. Kamminga, C., Wiersma, H. & Dudok van Heel, W.H. 1983. Investigations on cetacean sonar VI. Sonar sounds in Orcaella brevirostris of the Mahakam River, East Kalimantan, Indonesia; first descriptions of acoustic behaviour. Aquat. Mamm. 10: 83-94. Kreb, D. 1999. Observations on the occurrence of Irrawaddy dolphin, Orcaella brevirostris, in the Mahakam River, East Kalimantan, Indonesia. Z. Saug. 64: 54- 58. Leatherwood, J.S. 1996. Distributional ecology and conservation status of river dolphins (Inia geoffrensis and Sotalia fluviatilis) in portions of the Peruvian Amazon. Ph.D. Thesis, Texas A & M University, Texas, USA. 232 pp. MacKinnon, K., Hatta, G., Halim, H. & Mangalik, A. 1997. The ecology of Kalimantan. The ecology of Indonesia series 3. Oxford University Press. 152 pp. Martin, A.R. & Da Silva, V.M.F. 2000. Aspects of status of the Boto Inia geoffrensis in the central Brazilian Amazon. Paper, SC/52/SM15, presented at 52nd Annual Meeting of the International Whaling Commission, Small Cetacean Sub-committee.
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Priyono, A. 1994. A study on the habitat of Pesut (Orcaella brevirostris Gray, 1866) in Semayang-Melintang Lakes. Media Konservasi 4: 53-60. Reeves, R.R., Smith, B.D. & Kasuya, T. (eds), 2000. Biology and conservation of freshwater cetaceans in Asia. Occasional Paper of the IUCN Species Survival Commission, 23, IUCN, Gland, Switzerland. 152 pp. Smith, B.D., 2000. Review of river dolphins, genus Platanista, in the South Asian subcontinent. Paper, SC/52/SM4, presented at 52nd Annual Meeting of the International Whaling Commission, Small Cetacean Sub-committee. Smith, B.D., Ahmed, B., Ali, M.E. & G. Braulik, 2001. Status of the Ganges River dolphin or shushuk Platanista gangetica in Kaptai Lake and the southern rivers of Bangladesh. Oryx, 35: 61-72. Smith, B.D. & Hobbs, L. 2002. Status of Irrawaddy dolphins Orcaella brevirostris in the upper reaches of the Ayeyarwady River, Myanmar. Raffles Bull. Zool., Suppl. 10: 67-73. Smith, B.D. & Reeves, R.R. 2000. Survey methods for population assessment of Asian river dolphins. In: Biology and conservation of freshwater cetaceans in Asia. Occasional Paper of the IUCN Species Survival Commission 23: 97-115. IUCN, Gland, Switzerland. Stacey, P.J. & Arnold, P.W. 1999. Orcaella brevirostris. Mammal. Spec. 616: 1-8. Vidal, O., Barlow, J., Hurtado, L.A., Torre, J., Cendon, P. & Ojeda, Z. 1997. Distribution and abundance of the Amazon River dolphin (Inia geoffrensis) and the Tucuxi (Sotalia fluviatilis) in the upper Amazon River. Mar. Mamm. Sci. 13: 427- 445.
58 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
CHAPTER 5
Abundance of freshwater Irrawaddy dolphins in the Mahakam River in East Kalimantan, Indonesia, based on mark- recapture analysis of photo-identified individuals
In press: Journal of Cetacean Research and Management, 2004
One photo-identified individual PM 34 with a distinctively shaped dorsal fin. During early 1999 and mid 2002, a total of 59 individuals were identified.
59 Chapter 5
ABSTRACT
From February 1999 until August 2002 c. 9000 km (840 hours) of search effort and 549 hours of observation on Irrawaddy dolphins (Orcaella brevirostris) were conducted by boat in the Mahakam River in East Kalimantan, Indonesia. Intended goal was to generate an estimate of total population size essential for conservation and management of this threatened freshwater dolphin population. An abundance estimate based on mark-recapture analysis of individuals photographed during separate surveys is presented here. Two different analysis methods, i.e. Petersen and Jolly-Seber methods were employed and compared with each other and with earlier estimates derived from strip-transect analysis and direct counts. These comparisons serve to evaluate the biases of each method and assess the reliability of the abundance estimates. The feasibility of video-identification is also assessed. Total population size calculated by Petersen and Jolly-Seber mark-recapture analysis, was estimated to be 55 (95% CL = 44-76; CV=6%) and 48 individuals (95% CL = 33-63; CV=15%). Estimates based on strip-transect and direct count analysis for one sampling period, which was also included in the mark-recapture analysis, were within the confidence limits of the Jolly-Seber estimate (Ncount = 35 and Nstrip = 43). Calculated potential maximum biases appeared to be small, i.e. 2% of N for Petersen and 10% of N for Jolly-Seber method, which is lower than the associated CVs. Also, a high re-sight probability was calculated for both methods varying between 65% and 67%. Video images were considered a valuable, supplementary tool to still photography in the identification of individual dolphins in this study. For future monitoring of trends in abundance using mark/ re-capture analyses, a time interval is recommended between the two sampling periods that is short enough to minimise the introduction of errors due to gains and losses. Also, survey area coverage during photo-identification should be similar to avoid violation of the assumption of equal capture probabilities. The alarmingly low abundance estimates presented here call for immediate and strong action to preserve Indonesia’s only known freshwater dolphin population.
RINGKASAN
Dari Februari 1999 sampai Agustus 2002 kurang lebih 9000 km (840 jam) penelitian dan 549 jam pengamatan lumba-lumba Irrawaddy (Orcaella brevirostris) dilakukan dengan menggunakan kapal di Sungai Mahakam, Kalimantan Timur, Indonesia. Tujuan utamanya untuk menghasilkan suatu perkiraaan dari jumlah keseluruhan populasi yang digunakan sebagai bahan untuk perlindungan dan pengelolaan lumba- lumba air tawar dari kepunahan. Perkiraan keadaan yang berlebihan didasarkan pada
60 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam analisa penandaan-ulang dari potret individu selama survey terpisah dilaksanakan. Dua metode analisa, yaitu metode Petersen dan Jolly Seber digunakan dan dibandingkan satu dan lainnya dan dengan perkiraan awal yang diperoleh dari analisa strip-transect dan perhitungan langsung. Perbandingan digunakan untuk evaluasi penyimpangan dari masing-masing metode dan mendapatkan taksiran yang dapat dipercaya dari jumlahnya. Kemungkinan identifikasi dengan video juga dipergunakan. Perhitungan ukuran populasi total dengan metode analisa penangkapan kembali Petersen dan Jolly Seber, telah diperkirakan menjadi 55 (95 % CL = 44-76; CV= 6%) dan 48 ekor (95% CL=33-63; CV=15%). Perkiraan didasarkan pada metode strip- transect dan penghitungan langsung untuk periode pengambilan contoh, dimana termasuk juga dalam analisa penandaan dengan penangkapan kembali, berada dalam batas keyakinan dari perkiraan Jolly-Seber (Ncount=35 and Nstrip=43). Perhitungan penyimpangan potensial maksimum kelihatan lebih kecil, yaitu 2% dari N untuk Petersen dan 10% N untuk metode Jolly-Seber yang mana lebih rendah dari CV yang terkait. Juga suatu kemungkinan pengamatan kembali yang diperhitungkan untuk dua metode adalah berbeda antara 65% dan 67%. Gambar-gambar video dianggap sebagai hal berharga, sebagai alat bantu gambar potret dalam mengidentifikasi individu lumba- lumba pada penelitian ini. Untuk pengamatan yang akan datang dari kecenderungan dalam jumlah menggunakan metode penandaan-penangkapan kembali, jarak waktu yang disarankan antara dua periode pengambilan contoh adalah cukup pendek untuk mengurangi kesalahan awal berkaitan dengan pencapaian dan kehilangan. Juga cakupan daerah survei selama identifikasi foto harus sama untuk menghindari kesalahan dari kemungkinan penangkapan yang sama. Rendahnya tingkat perkiraan jumlah yang disajikan di sini adalah untuk dapat dengan segera diambil tindakan yang tegas dalam melestarikan satu-satunya populasi lumba-lumba air tawar di Indonesia yang telah diketahui.
INTRODUCTION
Since 1970, photo-identification studies have proven to be a valuable tool in revealing aspects of population dynamics, social organisation, distribution and movement patterns for many species of cetaceans (Whitehead et al., 2000). The technique involves collecting and cataloguing photographs of dolphins with distinctive marks on the dorsal fins, flukes and bodies that allow for identification of individuals. Photo- identification, when seriously attempted, was found feasible for every cetacean species that is in possession of a distinct dorsal fin (Mann, 2000). But the ease of getting good photo-identification results highly varies among species depending on uniqueness of the marks and behaviour of the species. Easily identifiable cetaceans with nearly complete photo-identification databases for certain populations include killer whales, 2000). For most other species, e.g., hump-backed dolphins, Sousa chinensis (Jefferson
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Orcinus orca (Baird, 2000) and humpback whales, Megaptera novaeangliae (Clapham, and Leatherwood, 1997; Jefferson, 2000); Pacific white-sided dolphins, Lagenorhynchus obliquidens (Morton, 2001) and northern bottlenose whales, Hyperoodon ampullatus (Gowans and Whitehead, 2001) only a proportion of the population can be reliably identified because not all fins are characteristically marked. Another factor limiting identification is due to the elusive behaviour of some species of dolphins. Photo- identification of Irrawaddy dolphins, Orcaella brevirostris, commonly described as an elusive species (Lloze, 1973; Dhandapani, 1992; Kreb, 1999) required greater effort, but was shown to be feasible for coastal populations in Australia (Parra and Corkeron, 2001). In addition, freshwater populations of Irrawaddy dolphins that are known to occur in only three major river systems, i.e. the Mahakam River in Kalimantan, the Mekong River in Vietnam, Laos and Cambodia and the Ayeyarwady River in Myanmar (Burma) were reported to be visually identifiable, but photo-identification efforts until now were more or less incidental (Stacey, 1996; Smith, 1997; Kreb, 1999). Freshwater dolphin populations in many cases live in a closed system and have no exchange with coastal populations. Thus, photo-identification and subsequent mark- recapture analysis to determine total population size might be feasible. This study reports on photo-identification of a population of Irrawaddy dolphins in the Mahakam River, Indonesia and is the first attempt to provide a catalogue in which most individuals of an entire freshwater Irrawaddy dolphin population are identified. The Irrawaddy Dolphin Orcaella brevirostris is a facultative freshwater dolphin, occurring both in shallow coastal waters and large river systems in tropical South East Asia and subtropical India (Stacey and Arnold, 1999). Irrawaddy dolphins in Indonesia occur along several coastlines and in one river in East Kalimantan, the Mahakam, where they are referred to as pesut (Kreb, 1999). The species is fully protected by law in Indonesia since 1990 and is adopted as a symbol of East Kalimantan Province. Their IUCN status was raised from ‘Data Deficient’ to ‘Critically Endangered’ based on data related to abundance collected from 1999 until 2000 (Kreb, 2002; Hilton- Taylor, 2000). The objectives are: to present an estimate of total population size based on photo-identification of individual dolphins by using different mark-recapture methods and to compare these with earlier estimates of abundance from strip-transects and direct counts (Kreb, 2002). In addition, the feasibility of digital video recordings as a tool to identify dolphins is evaluated. This photo-identification study is part of a long- term conservation and research project, begun in 1999 to provide a framework to protect the freshwater Irrawaddy dolphin population in the Mahakam River in East Kalimantan, Indonesia.
SURVEY METHODS
During the study period from February 1999 through August 2002, 12 surveys were conducted. Six extensive monitoring surveys (mean duration 20 days; SD= 4 days) covered the entire distribution range and six (mean duration 12 days; SD = 3 days)
62 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
were conducted in areas of high dolphin density (Figure 1). Extensive surveys were conducted with 12-16 m long motorised vessels (between 12 and 21 hp), travelling at an average speed of 10 km/ hr. The average observation time and photographic effort during the extensive monitoring surveys was one hour per sighting. Most intensive monitoring surveys involved attempts to follow one group for an entire day, with daily alternation of groups and using a small, motorised canoe with 5hp outboard engine. Photographic effort was spread out over the observation time (average duration 7 hours; range 1.5 -13 hours). Upon sighting, the group was approached to a minimum distance of 30m in order to take photographs and video images. We always tried to take these photos from similar angles, i.e. perpendicularly to the dolphins’ dorsal fin region. In addition, identification marks were recorded on datasheets. For each sighting, the duration, location, group behaviour, group size, group composition and environmental data were collected. Four age classes were defined: i) “neonates” were individuals of less than 1/2 the average length of an adult, which spent all their time in close proximity to an adult and exhibited an awkward manner of swimming and surfacing; ii) “calves” were animals between 1/2 and 3/4 the average length of an adult and which still spent most of their time in close proximity to an adult; iii) “juveniles” were animals of 3/4 the average length of an adult and which swam independently; iv) “ adults were individuals larger than an estimated 2 meters in length. Photographs were made by the author using a Canon EOS 650 camera body with a Sigma 300mm/ f4.0 lens, occasionally attaching a 1.4 teleconverter, effectively making it a 420mm/ f5.6 lens. Manual focus was always used with shutter speeds of 1/250 to 1/1500 of a second. Some 75% of the photo-id images were made with slide films using Sensia Fujichrome 100 ISO and another 25% were made using Fuji Superia 200 ISO print-films. It was attempted to always photograph every individual within the group irrespective of whether they at first sight appeared to have distinct dorsal fin markings or not. Photographs were generally taken perpendicularly to the dolphins’ dorsal fin region. Additionally, drawings of dorsal fins (made by aid of binoculars) were made by observers who did not take photographs. Dolphin age classes were also noted for each drawing. Direct observations and drawings were matched with a field photo-identification catalogue and assigned an existing or new identification code. One field-assistant was assigned to the task of making simultaneous video footage using a Sony VX 1000 digital camcorder with 10x optical and 20x digital zoom. Nearly always only the10x optical zoom was employed or better image quality. The auto- focus option was usually preferred since manually focusing proved more difficult with the camcorder than with the photo-camera. Information on the number of dead dolphins during the entire study period and in particular between the two sampling periods, was obtained through our own observations and from local, reliable reporters.
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Kedang Rantau Muara Kaman Loa Kulu Kota Bangun Kedang Kepala Batuq Semayang empang J Melintang Tepian Ulak Muara Pahu bution area, b) areas of high dolphin density and c) coastal Irrawaddy dolphin area. Muara Jelau Bohoq 64 Rambayan Muyub Ulu Damai Datah Bilang Kedang Pahu Muara Benangak
Long Bagun Ratah Figure 1. Study area with a) total dolphin distri Chapter 5 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
ANALYSIS
Photographs and slides were selected by aid of an 8x loupe for their good image quality, i.e. focus, glare, photographic angle, dorsal fin size coverage in image and catalogued on basis of identifiable features. Distinctive features noted included notches, scars and cuts on the dorsal fin and distinct fin shapes. Pigmentation patterns were only secondarily considered if they could be linked to a distinct fin shape. Pigment spots or areas do not occur symmetrically on both sides of the dorsal fin. In addition, it was found that pigmentation patterns on the bodies of dolphins and likely therefore on dorsal fins were not stable during the study period. Each photograph in the photo-identification catalogue corresponded to an identified individual and held information on the date, time and location at which the picture was taken as well as data on group size and composition. Photographs with distinctive features such as scars, cuts and humps on the dolphin’s bodies were also selected, but catalogued under another identification code. Photographs with distinctive body features alone were only used for mark-recapture analysis if they could be linked to an individual, which was already identified based on its dorsal fin. Identifications that were obtained through direct observation and drawings were kept in a separate database file than the photo-identified dolphins. These identifications were not used for the mark-recapture analysis. For analysis of recorded video-images, each image of a dorsal fin was played in slow-motion and paused. Similar to the photo-identification analysis, only images of good quality were selected. These good images were then compared with individuals from the photo-identification catalogue and these were given an identification code and put into a video-identification catalogue together with related sighting data. Two estimates of total population size (N) were calculated based on two different mark-recapture analysis methods of photo-identification data. Only sampling periods with extensive area coverage were selected, which were suitable for estimating total population size. The first estimate utilized the Petersen method for closed populations, involving one session of catching and marking and one recapture session. Bailey’s modified estimator was applied for sampling with replacement (Equation 1.1) (Hammond, 1986). Sample periods May/ June 2000 and August 2001 were chosen because the photographic effort (i.e. area coverage) was similar in those periods (Table 1). The second method to estimate total abundance was the Jolly-Seber method for open populations, allowing for gains and losses within the sampling periods. Also, capture histories of each identifiable individual were needed since the method requires both knowledge of the number of animals in each sample that were previously marked and information on the most recent previous sample in which each of them was last trapped. The number of marked individuals in four sampling periods, i.e., October 1999, May/ June 2000, January/ February 2001 and August 2001, with extensive area coverage, were higher than the minimum sample size of 10 marked individuals recommended to overcome imprecision of abundance estimates (Table 1) (Sutherland, 1996). Prior to the calculation of an abundance estimate, a goodness-of-fit test was
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applied (Sutherland, 1996) to test if animals differed in capture-probabilities, which may cause a serious bias of the estimate. After testing, three sampling periods were chosen to be appropriate for abundance estimation (see results). According to the Jolly-Seber method, no estimates of abundance can be calculated for the first and last sampling period and thus only one estimate is derived from the second sampling period (Equation 2.1). For this last method, it was also possible to calculate the proportion of the population surviving (Φ) from the 1st to the 2nd sampling occasion (Equation 2.3). A correction factor was applied to the population estimates of both methods to correct for the proportion of dolphins that are not identifiable (p) (Jefferson & Leatherwood, 1997). These were neonates and calves, which could not be captured properly on photo because their mothers protect them away from the boat and from a good camera angle and because calves often surface very suddenly (high arch dives). The averages of the proportion of neonates and calves encountered during two (Petersen) and three (Jolly-Seber) sampling periods are 10% and 8% respectively, which represent the proportion unidentifiable dolphins (p). For the Petersen method binomial 95% confidence intervals were calculated for the fraction of marked individuals (m2 + 1)/ (n2 + 1), which were then applied to the formula in Equation 1.1. to obtain the 95% confidence limits for population size (Krebs, 1999). Jolly-Seber confidence limits were calculated using the formula provided by Manly (1984). Coefficients of variation were calculated for both methods according to the formulas in Equation 1.2 and 2.4. Estimated re-sight probabilities for the Petersen estimator are given by m2/ n2 and p2 = m2/ n1 and for Jolly-Seber by ni/ Ni, in which Ni is (only here) the uncorrected abundance estimate for proportion of identifiable dolphins.
( ) Eqn 1.1 n2 + 1 (Petersen method) N = n 1 ( ) ( − ) m 2 + 1 1 p
2 − 1 n ( n + 1 ) ( n − m ) v a r ( 1 − p ) Eqn 1.2 C V ( N ) = N 1 2 2 2 + 2 2 ( ) ( ) ( − ) m 2 + 1 m 2 + 2 1 p
where n1 = number identified on the first occasion n2 = total number identified on the second occasion
m2 = number of identified dolphins found on the second occasion p = proportion of unidentifiable individuals
( ) M i n i + 1 Eqn 2.1 N i = (Jolly-Seber method) ( m i + 1 ) ( 1 − p )
66 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
( ) m i + R i + 1 z i Eqn 2.2 Mi = ( r i + 1 )
Eqn 2.3 Φ M i + 1 i = ( M i − m i + R i )
Eqn 2.4
− ( − ) ⎛ M i m i + R i + 1 ⎞ ⎛ 1 1 ⎞ 1 1 v a r 1 p ⎝ ⎠ ⎝ − ⎠ + − + ( ) ( ) 2 M i + 1 r i + 1 R i + 1 m i + 1 n i + 1 ( 1 − p ) CV ( N i ) = x ⋅ i − ⎛ 0.5 3 n i ⎞ lo g e N i + 0.5 lo g e ⎝ ⎠ 8 N i
Where Ni = population size at the time of the ith sample Mi = number of marked animals in the population when the ith sample is taken (excluding animals newly marked in the ith sample) ni = total number of animals caught in the ith sample Ri = number of animals that are released after the ith sample mi = number of animals in the ith sample that carry marks from previous captures zi = number of animals caught both before and after the ith sample but not in the ith sample itself ri = number of animals that were released from the ith and were subsequently recaptured xi = number of samples
Finally, maximum biases that may affect population size estimates for each method were calculated. A maximum bias using Petersons method, which assumes no losses, was calculated by adding the number of dead dolphins (= 3) in between the two sampling periods, to the number of ‘recaptured’ animals during the second sampling period (m2bias= m2 + 3). This number was also added to the total number caught on the second occasion (n2bias= n2 + 3). When applying this bias one assumes that these dolphins would have been ‘marked’ during the first session and also assumes that they would have been ‘recaptured’ if they hadn’t died. A maximum bias using Jolly-Seber method was related to the fact that one area was not surveyed during the second sampling period of the three sampling periods in total. This area, which is an area in between two rapids and home to a group of six dolphins, was surveyed only during the first and last sampling period. Two and three new individuals were marked during the first and last sampling period, respectively, without any recaptures. The largest deviation from the abundance estimate would apply for a situation in which we assume that this area would have been surveyed during the second sampling period, which four new individuals would be captured and marked and three of which would be recaptured during the third sampling period.
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This maximum deviation of the estimate is calculated following equation 2 above by adding three individuals to r2 (number of marked dolphins in the 2nd sample, which were recaptured in the 3rd sample) and four individuals to n2 and R2 (total number caught and released in the 2nd sample). Variable z2 is not affected by the missing survey effort during the second sampling period because the individuals marked in that area were not similar during the first and last sampling period. Conclusively, this maximum bias holds only if the following assumptions are true: None of the two individuals marked during the first sampling period would be recaptured if the ‘missed’ area was surveyed during the second sampling period. Four individuals would be marked during the second sampling period so that r2bias = r2 + 3, n2bias = n2 + 4 and R2bias = R2 + 4.
RESULTS
Estimates of abundance based on photo-identification mark-recapture analysis
During the entire study period from February 1999 until August 2002, a total of 2074 photographs were made during 83 days of which 1499 (partially) portrayed dolphins and 558 (27%) failed, showing merely circles in the water (Table 1). Of the dolphin photographs, 753 photographs (50%) were selected for photo-identification because of good image quality. Some 728 photographs showed identifiable features on dorsal fins, sometimes in combination with other characteristic traits on the dolphins’ bodies, producing an average of almost 9 identifiable dorsal fin photographs per day. An additional number of 25 photographs only showed identifiable features on the dolphins’ bodies. As such, a total of 59 individual dolphins were catalogued based on dorsal fin identification. Four individuals are shown in Plate 1. Within the four initially chosen sampling periods for the Jolly-Seber method, animals appeared to differ significantly in capture-probabilities (G = 10.06; d.f. = 2; P < 0.01), meaning that the underlying assumptions (see discussion) of the method were violated. The bias was consequently rendered insignificant by only using sampling periods, which include a high proportion (i.e. over 50%) of the population. Therefore, sampling period October 1999 was removed from analysis, which included only 31% of the Petersen population estimate. Another G-test for the remaining periods revealed that this time no assumptions were violated (G = 1.8; d.f. = 1; P = 0.17). The number of dolphins identified on photograph for each sampling period (ni) are presented in Table 1. For both Petersen method applies that the number of dolphins that were identified in the first period (May/ June 2000) and recaptured on photograph during the second period (m2) (August 2001) is 22 individuals.
68 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
Table 1. Photo-identification success rate and discovery rate of new individuals.
Year Survey period Survey area No. dolphin No. identified No. different No. of new coverage photographs dorsal fins individuals (ni) individuals 1999 Fe/ Ma E 25 3 2 2 Ap/ May E 25 7 5 5 Oc E 49 28 16 13 2000 May/Jun E 206 90 33 21 Au I 157 83 24 4 Nov I 65 23 16 1 2001 Ja/Fe E 175 82 29 6 Jun/Jul I 267 127 37 1 Au E 178 90 34 3 Oc/No I 89 36 23 1 2002 Ap I 181 102 28 1 Au I 82 54 23 1 Total 12 periods 1499 728 59
E = Extensive monitoring survey in entire dolphin distribution area; I = Intensive monitoring survey in high dolphin density areas.
Plate 1. (left above:) PM 2; (right above:) PM 1; (Left below:) PM 8; (Right below:) PM 3
For Jolly-Seber method applies that m2 is 14 individuals (using periods May/ June 2000 and January/ February 2001). The estimated re-sight probabilities for Petersen method are 65% and 67% and for Jolly-Seber method is 66%. The number of dolphins that were re-captured on photograph in the third sampling occasion (Jolly-
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Seber) and identified during earlier occasions (m3) is 28 individuals, illustrating the high re-sight probability over more than two sampling periods. The estimate of total population size using the Petersen two-sample mark-recapture method was 55 individual dolphins (95% CL = 44 – 76; CV = 6%). Calculating a potential maximum bias due to loss of individuals between the sample periods, lowers the estimate to 54 individuals (95% CL = 44 -76; CV = 10%), which is 2% of the estimated population size above. During the 3.5 year study period at least 17 dolphins have died but the specific dolphin identities were not available and thus could not be traced back to the photo-identification catalogue. An estimate of population size using the Jolly-Seber method arrives at 48 individual dolphins (95% CL = 33 - 63; CV = 15%). The proportion of the population surviving from the 1st to the 2nd sampling occasion is 66%. Reported number of dead dolphins between these two sampling periods is 2 individuals (4% of N2). An estimate was also calculated including a maximum bias due to lack of survey effort during one of the sampling periods in one ‘closed’ area that is inhabited by a group of six dolphins. This corrected estimate arrives at 53 individuals (95% CL = 36 – 64; CV = 19%), which is 10% of the unbiased population size.
Selected pictures 70 160 Identified dolphins 60 140 Cumulativ e 120 identified dolphins 50
100 40 80 30 60 20 40 Cumulative numberidentified 20 10 0 0
Oc Au Nov Au Ap Au Ja/Fe Fe/Mar Jun/Jul Oc/ No Ap/May May /Jun 1999- 2000- 2001- 2002- Survey period
Figure 2. Discovery rate of new individuals and number of identified dolphins per survey period in relation to the number of selected pictures
Figure 2 shows the cumulative number of new individuals identified in different survey periods in combination with photographic success in obtaining identifiable pictures of dorsal fins for each sub-period. The cumulative curve begins to level of after the August 2001 survey period and during the next three survey periods only one
70 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
individual was added each time (Table 1). Some 95% of the individuals of the photo- identification catalogue are identified in the period March 1999 until August 2001. After that date a plateau in the number of new identifications is more or less reached, with only a yearly 5% increase of new identifications (three individuals) of the total photo-identification catalogue. With an annual birth rate of 10.5 % of the total population, this yearly 5% increase in new identifications is within this birth rate range and may therefore be attributed to possible neonates. It should be noted though that these neonates can be identified only when they are over one-year of age, since they are otherwise difficult to photograph. So, the new identifications within any one year may include last year’s neonates i.e., one year old calves. The plateau was not a result of low photographic effort, since the number of new individuals added to the catalogue is not correlated with the number of identifiable photographs (r = 0.06; DF = 10). Some 98% of the identified dolphins were recaptured on photograph on at least two different days and 90% were recaptured during at least two different survey periods (Figs 3 and 4). Individual dolphins were recaptured on a mean number of 7.0 different survey days (± SD = 4.7) and 4.5 survey periods (± SD = 2.4). Individual dolphins were recaptured on a maximum of 21 days and 10 survey periods (Plate 2).
Plate 2. Example of a low quality photograph (small dorsal fin image), in which dolphin PM01 can still be identified over larger distances due the distinctiveness of its mark. Dolphin PM01 was photographed during 21 different survey days, on 41 pictures and photographed here on 23/8/00 (upper picture) and 2/7/01 (lower picture).
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16
14
12
10
8
6
4
Number of re-sighted individuals 2
0 12345678910 Number of survey periods
Figure. 3. The number of re-sighted individuals during a number of survey periods, e.g. 14 individuals were re-sighted during four different survey periods.
16
14 No. of dolphins re-sighted on photograph on x days 12 No. of dolphins re-sighted on video on x days 10
8
6
4
2
0 1 3 5 7 9 111315171921 Number of survey days
Figure. 4. The number of re-sighted dolphins on photograph and video over a maximum of 21 days, e.g. 14 and 11 dolphins were re-sighted on photograph and video respectively during a period of 2 until 3 days.
72 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
Feasibility of video-identification
Video recordings were made during seven different survey periods and 21 days. Total recording effort to get photo-identification images was 8.8 hours. Identifiable dorsal fins of surfacing dolphins were recorded on 79 video-images, from which 31 different individuals could be identified. On average, 9.0 identification images per hour and 4 images per day recording were produced. Four individuals were identified based on body marks alone. Fifty-two percent of the individuals were encountered on more than one day (mean = 2.1; ± s.d. 1.4; range = 1 – 5) (Figure 4).
DISCUSSION
Estimates of abundance based on photo-identification mark-recapture analysis
Violated assumptions and biases Two methods for analysing mark-recapture results of photo-identified dolphins were used in this study, the Petersen two-sample method and Jolly-Seber method. The first method was found appropriate because during two of the 12 survey-periods the following required condition to obtain an estimate of total population size was met: photographic ‘trapping’ effort was equally spread over the entire dolphin distribution range, so that all animals have the same probability of being identified (assumption 2, see below). Most other survey periods involved intensive monitoring surveys in areas of high dolphin density only. Also, one area in between two rapids was not surveyed during the other extensive monitoring surveys due to bad weather conditions. The second method (Jolly-Seber) was applied because it allowed for gains and losses between the sampling periods. The disadvantages of using these methods are that they rely on underlying assumptions, which, if violated, produce serious biases of the results. For the Petersen method, these assumptions are: 1) the population is closed; 2) all animals have the same probability of being caught; 3) marking does not affect the catchability of an animal; 4) the second sample is a simple random sample; 5) animals do not lose their marks; and 6) all marks are reported on recovery. For the Jolly-Seber method, assumption 2 and 5 from Petersen are also relevant. Additional assumptions for Jolly-Seber are that: 7) every marked animal has the same probability of surviving from the ith to the (i + 1)th sample; 8) every animal caught in the ith sample has the same probability of being returned to the population; 9) all samples are instantaneous (Hammond, 1986). The first and second assumptions are being violated in this study regarding the Petersen method and Jolly-Seber method, respectively, and the effects are discussed below. The first assumption of the Petersen method was violated as three dolphins (identity unknown) had died and four dolphins were born between the sampling periods. However, mortality is not likely to influence n2 (total number caught on the
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second occasion), since during each sampling period only 55-57% of total photo- identification catalogue was captured on film. A possible influence of dead dolphins on the m2 (number of ‘marked’ animals recaptured on the second occasion) likely occurred although not unalterably, since the number of ‘recaptured’ animals is not equal (only 64-66%) to the total number of individuals caught on the first and second occasions. So, these dead dolphins of unknown identity could just as well not have been ‘marked’ on the first occasion or, if they were, had not been recaptured. Still, the three dead dolphins may possibly have produced a biased estimate and therefore a correction was calculated for this bias, which decreased the estimate at the most by two individuals. This bias only applies if we assume that these three dolphins were ‘marked’ at the first occasion and presumably would have been caught on the second occasion as well if they hadn’t died. In that case, the abundance estimate would be 54 individuals, within the confidence limits of the abundance estimate of 55 individuals as inferred in the results section. This small difference may be a result of the fact that a high proportion of the estimated population was captured during each sampling period (65-67%), since catching over 50% of the population limits biases that may arise through assumptions being violated (Sutherland, 1996). Similar to mortality, recruitment (dolphins born in the period between the two sampling periods) is not likely to influence the overall number of dolphins caught on the second occasion (n2). Furthermore, neonates will not influence the number of ‘marked’ animals found on the second occasion (m2), since they were born after the first sampling period and were thus not recorded. Neonates and calves have a low chance of being identified at all since they surface very irregularly and briefly during the first few months and are hard to photograph as they swim very close to the mother. Consequently, neonates encountered in the first sampling period will most certainly not have been ‘marked’ and will for that reason also not affect one of the variables of the Petersen formula. Violations of the second assumption due to heterogeneity between dolphins in catchability and trap responses were tested with a goodness-of-fit-test for three sampling periods used within both analysis methods and this revealed that there was no difference in capture probabilities except for the neonates and calves for which a correction factor is applied to calculate abundance estimate (see analysis). This is in contrast to most other cetacean photo-identification studies in which unequal capture probabilities are often the case due to variation in individual behaviour, such as wariness of boats or fluking behaviour, that affect the probability of obtaining good photographs (Whitehead, et. al., 2000). Capture probabilities are more likely to vary for bow-riding dolphins, whereas the dolphins in this study were all photographed from some distance of the boat. Thus, boat-shyness or attraction did not play as much of a role. Since photo-identification is in principal a non-invasive technique, any issues of trap responses are not relevant here. In spite of the fact that dolphins in principal had an equal probability of being photographed, differences in distinctiveness of marks and in survey area coverage may cause capture probabilities (obtaining identifiable
74 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
images) to vary among individuals and cause a bias of the estimate of population size (Gowans & Whitehead, 2001). Although all photographs of good image quality yielded identifiable marks, photographs of less quality (smaller images) were only identifiable for those individuals with very distinct marks (Plate 2). Other markings needed to fill a significant part of the frame for identification and therefore more slides were discarded for use in connection with these features. Another bias in capture probability was related to differences in survey area coverage for each sampling period in the calculation of the Jolly-Seber estimate. However, the G-test result and the high percentage of re-sightings over different survey days and periods (95% and 90% of total identified individuals were re-sighted over two days and periods or more, respectively), indicate that the bias is not large, possibly due to the fact that a large part of the population was caught during both samples, as stated earlier. Nevertheless a maximum bias was calculated that could affect the Jolly-Seber estimate for the difference in area coverage. This bias produced an estimate that only differed with three individuals from the Jolly-Seber estimate. Finally, dolphins in this study were only identified using natural marks, which would be stable over long sampling intervals (such as notches, cuts, scars and fin shapes) to prevent biases when marks are lost (such as pigmentation patterns) as suggested by Gowans & Whitehead (2001). Furthermore, other underlying assumptions of both methods did not seem problematic in this study. The difference between the total number identified dolphins (59) and the estimated total population size (N= 48-55), may be explained by the fact that the first number was derived over a 3.5 year study period, during which 17 dolphins had died. The total number identified dolphins does therefore not represent an abundance estimate. The proportion of the population surviving from the 1st to the 2nd sampling occasion (66%) based on the Jolly-Seber equation whereas the proportion surviving based on the reported number of dead dolphins between these two sampling periods is 96%. The difference may be explained in the fact that the probability of survival within Jolly-Seber is determined by sampling the marked population only and variation in the size of the marked population may occur between two sampling periods for reasons other than mortality and emigration. For example, photographs are not always successful for all sightings within each sampling period due to the dolphins’ group behaviour at that specific moment, which may vary through time for the same group. In this way, some groups may be missed from identification during one period but identified during another period.
Identifiability As stated above, in this study, from all photographs of good image quality of dorsal fins, individual dolphins could be identified. This agrees with a photo-identification study on coastal Irrawaddy dolphins in North Queensland, Australia, although juveniles were reported to lack any distinctive features to allow for identification (Parra and Corkeron, 2001). Of Pacific white-sided dolphins, Lagenorhynchus obliquidens
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and Indo-Pacific humpbacked dolphins, Sousa chinensis, only a percentage of dolphin dorsal fins could be identified (Jefferson and Leatherwood, 1997; Morton, 2000). In addition, as in the Australian study, no standardized identification measure could be used such as the Dorsal Fin Ratio (Defran et al., 1990) to identify Irrawaddy dolphins in the Mahakam, since fins lacked clearly distinct top and bottom points. In contrast to the studies mentioned above on other species than Orcaella brevirostris, Irrawaddy dolphins in this study and others could also be identified based on the variation of dorsal fin shapes (Stacey, 1996; Parra and Corkeron, 2001). With regard to possible false matches: I only found three dolphins with more uniform, smooth dorsal fin shapes (although not similar compared to each other). However, each of these dolphins were only re-sighted on 5, 7 and 11 different survey days, which is within the standard deviation of the mean number of days on which all dolphins were re-sighted (mean = 7 days, SD = 4.7). So, the chance seems small that different dolphins were identified as one of these three dolphins. Then I would expect the number of sighting days for these dolphins to be much more numerous. Also, I found these fins still identifiable on basis of overall shape, even though characteristic notches were missing. With regard to identification of calves and juveniles, I found that Irrawaddy dolphins in the Mahakam River did have identifiable features on their dorsal fins. This stands in contrast to Parra and Corkeron (2001), who conducted a photo- identification study of coastal Irrawaddy dolphins in Australia and found that calves and juveniles did not have any distinctive features to allow identification. During each of the extensive sampling periods (covering entire dolphin distribution range), we encountered one group of animals consisting of some six juveniles without adults. Unfortunately, individuals of these groups were never successfully photographed, because of their elusive surfacing-behaviour. Only drawings of dorsal fins, (made by aid of binoculars) and one photograph with distinctive marks on the juvenile’s body were available for these. Juveniles in mixed groups were on the other hand much less shy, in fact they often surfaced near the boat. Since no record was kept in the field of the dolphin age classes of each photograph, it is not possible to trace which identified dolphin is a juvenile and which is an adult on basis of the picture alone. However, occasionally, when drawings were made during the study of several characteristic dorsal fins, age class was also noted and these included both juveniles and calves. The high percentage of individuals that were re-sighted on more than one occasion (98% of 59 identified dolphins) is an indication of the closeness of the Mahakam dolphin population. Percentage of re-sightings were similar (97% and 100%) for resident populations of marine tucuxis, Sotalia fluviatilis in Southern Brasil and of 21 identified bottlenose dolphins, Tursiops truncatus, in the Stono River estuary in South Carolina (Flores, 1999; Zolman, 2002). Resightings of seasonally occurring groups are typically lower; varying percentages of 32%, 50% and 57 % were found of 675 identified individual Pacific white-sided dolphins, Lagenorhynchus obliquidens, in the Broughton Archipelago, Canada, 35 identified Irrawaddy dolphins, Orcaella brevirostris, in Cleveland and Bowling Green Bay in North Queensland, Australia and 213
76 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
identified Indo-Pacific humpbacked dolphins, Sousa chinensis, in Hong Kong waters, respectively (Morton, 2000; Parra, 2001; Jefferson, 2000).
Comparison of different techniques to estimate population abundance The estimates of population size based on two different methods in this mark- recapture study are very much in agreement with each other since both estimates are within the confidence limits of each other (combined between 33 and 76). It may be noted though that the Petersen estimate (N = 55) is somewhat higher than the Jolly- Seber estimate (N = 48), whereas the coefficient of variation is smaller for the first estimate (CV = 6% and 15%). The latter estimate is close to the estimate derived from direct counts and strip-transects in May/ June 2000 (Ncount = 35 and Nstrip = 43) Kreb, 2002) with both estimates within the confidence limits of the Jolly-Seber estimate. Because the low estimates calculated here represent the total population size of dolphins in the Mahakam, immediate conservation measures are required to reduce the high minimum mortality rate of 10.5% dolphins of total population per year. Moreover, intended live-captures of dolphins for display in a local oceanarium to be built in the district’s capital city along the Mahakam should therefore definitely not be allowed for this small population. In order to monitor future trends in abundance, photo-identification may be a valuable tool. However, to increase precision and prevent biases due to gains and losses of individuals I recommend that photographs be taken during two extensive monitoring surveys in sequence covering the entire dolphin distribution range with a minimum time interval. Conclusively, since the results of the mark-recapture studies and direct count and strip-transect studies are very similar, future surveys to monitor trends in abundance of the latter type are feasible, if one needs to be cost efficient. However, surveys in combination with photo-identification are preferable in order to obtain data on long-term social system and migration patterns.
Feasibility of video-identification
The number of identifiable video-images per hour recording in this study (9 images/ hr), was much lower than those recorded in the video-identification study of bottlenose dolphins in South Carolina (Zolman, 2002), which yielded 31 images per hour recording time. This may be a result of the fact that in the latter study only a video was used for identification of dolphins, which may increase the efficacy to make good quality recordings. Another reason is that it may be more difficult to record dorsal fins of Irrawaddy dolphins because of their shy and irregular surfacing pattern (Kreb, 1999). Also, the number of identifiable video images per day were much lower i.e., four identifiable video images per day, in comparison to the still photography in this study, which produced nine identifiable photographs per day. Nevertheless, although the yield of identifiable images may be less than in other studies and in
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comparison to still photography, video-identification used as an additional tool has some advantages. First, in most cases the entire movement of the dolphin is visible, during play-back including all the different angles from which a dorsal fin can be seen. This was particularly useful in cases when there were any doubts within the photo- identification catalogue about whether two assumedly different identified dorsal fins belong in fact to one and the same individual. Although dorsal fin pictures were always attempted to be taken perpendicularly to the dolphins body axis close to the dorsal fin region, small deviations from this angle could in some cases cause confusion about the identification. Second, this technique can link body characteristics to individuals, which are initially identified based on dorsal fins alone. Third, for other purposes, such as study of social structure, video-recordings make it possible to record the physical position of individual dolphins with regard to each other. However, disadvantages of the use of a video camera were experienced by author and field- assistants in connection with the slow adjustment between wide-angle and zoom modes. Even though we tried to use a fixed zoom length and estimated where the dolphins would surface, the manoeuvrability of the video camera suffered in comparison with the photo-camera. In addition, the quality of video images for which a digital zoom was used often did not allow for accurate identification. Since the images were analysed by using the slow motion, or pause mode the quality of still video images decreased significantly as a consequence, as did images recorded with the optical zoom. No mark-recapture analyses were performed using video images, since the images were not recorded systematically throughout the study period. The quality of the still video images was found low in comparison to the photographs. Therefore, identifications were not directly based on the video images but were first traced back to the photo-identification catalogue. However, my overall conclusion is that video- identification in combination with photo-identification appeared to be useful for determining identities of individual dolphins.
ACKNOWLEDGEMENTS
I would like to thank Hardy Purnama, Zainuddin (BKSDA), M. Syafrudin, Achmad Chaironi, Ade Rachmad, Arman, M. Syoim, Budiono, Bambang Yanupuspita, Sonaji, Syahrani, Rudiansyah, Ahank, Iwiet, Hendra, Munadianto (Universitas Mulawarman Samarinda), Audrie J. Siahainenia, Ramon (Coastal Resource Management Program/ Proyek Pesisir Kal-Tim), Karen Damayanti Rahadi (Universitas Padjajaran), Pak Sairapi and Pak Muis for their assistance, enthusiasm and hard work. Funding for fieldwork was provided by Ocean Park Conservation Foundation, Hong Kong; Martina de Beukelaar Stichting; Stichting J.C. van der Hucht Fonds; Gibbon Foundation; Netherlands Program International Nature Management (PIN/ KNIP) of Ministry of Agriculture, Nature Management and Fisheries; Van Tienhoven
78 Mark-recapture analysis of photo-identified Irrawaddy dolphins in the Mahakam
Stichting; World Wildlife Fund For Nature (Netherlands); Amsterdamse Universiteits Vereniging; Coastal Resource Management Program/ Proyek Pesisir. I would like to thank the Indonesian Institute of Sciences (LIPI), the East Kalimantan nature conservation authorities (BKSDA), the General Directorate of Protection and Conservation of Nature (PHKA) for allowing me to conduct my research. The University of Mulawarman in Samarinda (UNMUL), Plantage Library, M. Lammertink and Dr. P.J.H. van Bree (University of Amsterdam (UvA), Zoological Museum Amsterdam) are thanked for their support and J. Van Arkel (Institute for Biodiversity and Ecosystem Dynamics (IBED) for producing the map figure. The manuscript was improved thanks to comments from Prof. F.R. Schram, Dr. Vincent Nijman (IBED, UvA), Dr. T.A. Jefferson (Southwest Fisheries Science Center, National Marine Fisheries Service, La Jolla) and one anonymous referee.
REFERENCES
Baird, R.W. 2000. The killer whale: foraging specializations and group hunting. In: Mann, J., Connor, R.C., Tyack, P.L. & Whitehead, H. (eds.) Cetacean societies. Field studies of dolphins and whales. Pp. 127-153. The University of Chicago Press, Chicago. Clapham, P.J. 2000. The humpback whale: seasonal feeding and breeding in a baleen whale. In: Mann, J., Connor, R.C., Tyack, P.L. & Whitehead, H. (eds.) Cetacean societies. Field studies of dolphins and whales. Pp. 173-196. The University of Chicago Press, Chicago. Defran, R.H., Schultz, G.M. & Weller, D.W. 1990. A technique for the photographic identification and cataloguing of dorsal fins of the bottlenose dolphin (Tursiops truncatus). Rep. int. Whal.Commn. (special issue) 12: 53-55. Dhandapani, P. 1992. Status of the Irrawaddy River dolphin Orcaella brevirostris in Chilka lake. Journal of the Marine Biology Association of India 34: 90-93. Flores, A.C. 1999. Preliminary results of a photo-identification study of the marine tucuxi, Sotalia fluviatilis, in southern Brazil. Marine Mammal Science 15: 840-847. Gowans, S. & Whitehead, H. 2001. Photographic identification of northern bottlenose whales (Hyperoodon ampullatus): sources of heterogeneity from natural marks. Marine Mammal Science 17: 76-93. Hammond, P.S. 1986. Estimating the size of naturally marked whale populations using capture-recapture techniques. Rep. int. Whal.Commn. (special issue) 8: 253-282. Hilton-Taylor, C. 2000. 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, U.K. Jefferson, T.A. and Leatherwood, S. 1997. Distribution and abundance of Indo-Pacific hump-backed dolphins (Sousa chinensis, Osbeck, 1765) in Hong Kong waters. Asian Marine Biology 14: 93-110.
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Jefferson, T.A. 2000. Population biology of the Indo-Pacific hump-backed dolphin in Hong Kong waters. Wildlife Monographs 144: 65pp. Kreb, D. 1999. Observations on the occurrence of Irrawaddy dolphin, Orcaella brevirostris, in the Mahakam River, East Kalimantan, Indonesia. Zeitschrift für Säugetierkunde 64: 54-58. Kreb, D. 2002. Density and abundance of the Irrawaddy dolphin, Orcaella brevirostis, in the Mahakam River of East Kalimantan, Indonesia: A comparison of survey techniques. The Raffles Bulletin of Zoology, Supplement 10: 85-95. Krebs, C.J. 1999. Ecological Methodology. Addison-Welsey Educational Publishers, Inc, US. 620 pp. Lloze, R. 1973. Contributions a l’étude anatomique, histologique et biologique de l’Orcaella brevirostris (Gray -1866) (Cetacea-Delphinidae) du Mekong. Dissertation thesis, Toulouse, France. [In French] Mann, J. 2000. Unraveling the dynamics of social life; long term studies and observational methods. In: J. Mann, R.C. Connor, Tyack, P.L. & Whitehead, H. (eds.) Cetacean societies. Field studies of dolphins and whales. Pp. 45-64. The University of Chicago Press, Chicago. Manly, B.F.J. 1971. A simulation study of Jolly’s method for analysing capture- recapture data. Biometrics 40: 749-758. Morton, A. 2000. Occurrence, photo-identification and prey of Pacific white-sided dolphins (Lagenorhynchus obliquidens) in the Broughton Archipelago, Canada 1984- 1998. Marine Mammal Science 16: 80-93. Parra, G.J. and Corkeron, P.J. 2001. Feasibility of using photo-identification techniques to study the Irrawaddy dolphin, Orcaella brevirostris (Owen in Gray 1866). Aquatic Mammals 27: 45-49. Smith, B.D., Thant, U.H., Lwin, J.M. & Shaw, C.D. 1997. Investigations of cetaceans in the Ayeyarwady River and northern coastal waters of Myanmar. Asian Marine Biology 14: 173-194. Stacey, P.J. 1996. Natural history and conservation of Irrawaddy dolphins, Orcaella brevirostris, with special reference to the Mekong River, Lao P.D.R. Unpublished M.Sc. thesis, University of Victoria, Canada. 123 pp. Stacey, P.J. and Arnold, P.W. 1999. Orcaella brevirostris. Mammalian Species 616:1-8. Sutherland, W.J. (ed) 1996. Ecological Census Techniques. A Handbook. Cambridge University Press, UK. 336pp. Whitehead, H., Christal, J. & Tyack, P.L. 2000. Studying cetacean social structure in space and time: innovative techniques. In: Mann, J., Connor, R.C., Tyack, P.L. & Whitehead, H. (eds.) Cetacean societies. Field studies of dolphins and whales. The University of Chicago Press, Chicago. Zolman, E.S. 2002. Residence patterns of bottlenose dolphins (Tursiops truncatus) in the Stono River estuary, Charleston County, South Carolina, U.S.A. Marine Mammal Science 18: 879-892.
80 Conservation of riverine Irrawaddy dolphins in Borneo
CHAPTER 6
Conservation management of small core areas: key to survival of a critically endangered population of riverine Irrawaddy dolphins in Borneo
Daniëlle Kreb and Budiono
In press: Oryx, 2004
Dolphins preference for fish-rich but human-crowded areas makes them vulnerable to many human-induced threats. Awareness campaigns therefore form a critical factor in their survival. Photo: Daniëlle Kreb
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ABSTRACT
In order to clarify the previous status of the facultative Irrawaddy River Dolphin, Orcaella brevirostris, in the Mahakam River in East Kalimantan, which was ‘insufficiently known’ following IUCN criteria, we collected data from early 1999 until mid 2002 on abundance, habitat use, population dynamics and threats relevant to the conservation of Indonesia’s only freshwater dolphin population. Our best estimates of total population size varied between 33 and 55 dolphins (95% confidence limits: 31- 76) based on direct counts, strip-transect analysis, and Petersen and Jolly-Seber mark- recapture analyses of photo-identified dolphins. Mean minimum annual birth and mortality rates were nearly similar, i.e. 13.6% and 11.4% and no changes in abundance > 8% were detected over 2.5 years. Dolphins primarily died after gillnet entanglement (73% of deaths). Dolphins’ main habitat includes confluence areas between the main river and tributaries or lakes. Dolphins daily intensively use small areas mostly including confluences, moving up and downstream over an average length of 10 km of river and within a 1.1 km2 - area size. These areas are also primary fishing grounds for fishermen and subject to intensive motorized vessel traffic. Sixty-four percent of deaths (from 1995-2001) with known location (n=36) occurred in these areas. Formal interviews with local residents revealed a generally positive attitude towards the establishment of protected dolphin areas. Because of the dolphins’ dependence on areas that are also used intensively by people, primary conservation strategies should be to increase local awareness and introduce alternative fishing techniques.
RINGKASAN
Dalam usaha memperjelas kondisi lumba-lumba Irrawaddy (Orcaella brevirostris) di Sungai Mahakam Kalimantan Timur, yang mana “belum banyak diketahui” berdasarkan kriteria IUCN, kami mengumpulkan data-data sejak awal tahun 1999 hingga pertengahan 2002 tentang jumlah, penggunaan habitat, perubahan populasi, dan ancaman yang berkaitan dengan upaya konservasi satu-satunya lumba-lumba air tawar di Indonesia. Diperkirakan jumlah populasi Pesut Mahakam berkisar antara 33 hingga 55 ekor (tingkat kepercayaan 95%: 31-76) berdasarkan perhitungan langsung, analisis strip-transek, dan analisis penandaan-ulang Peterson dan Jolly-Seber dari identifikasi foto lumba-lumba. Rata-rata terendah tingkat kelahiran dan kematian pertahun hampir sama yakni 13,6% dan 11,4% dan tidak ada perubahan jumlah lebih dari 8% selama 2,5 tahun. Kematian utama lumba-lumba adalah terperangkap rengge (73%). Habitat utama lumba-lumba termasuk pertemuan antara sungai utama dan anak sungai atau danau. Sehari-hari lumba-lumba secara intensif menggunakan daerah yang kecil kebanyakan merupakan daerah pertemuan sungai, bergerak ke hulu dan ke hilir dengan jarak tempuh rata-rata 10 km dan dalam ukuran areal 1.1 km2. Tempat- tempat ini juga daerah utama penangkapan ikan dan lalu lintas kapal bermotor. Enam puluh empat persen (64%) kematian (dari 1995-2001) dengan lokasi yang diketahui
82 Conservation of riverine Irrawaddy dolphins in Borneo
(n = 36) terjadi di daerah ini. Wawancara formal dengan penduduk lokal umumnya menyatakan sikap positif terhadap pembentukan daerah perlindungan lumba-lumba. Karena ketergantungan lumba-lumba pada tempat yang juga digunakan intensif oleh masyarakat, strategi utama konservasi adalah meningkatkan keperdulian dan memperkenalkan cara alternatif menangkap ikan kepada masyarakat lokal.
INTRODUCTION
River dolphins and porpoises are among the world’s most threatened mammal species. The habitat of these animals has been highly modified and degraded by human activities, often resulting in dramatic declines in their abundance and range (Reeves et al., 2000). Protection of freshwater dolphins and their habitat is a major challenge since river systems are the veins of human activities in terms of transport, fishing, and industrial processes, and are also heavily affected by forest fires, which were more likely to occur near rivers (Fuller & Fulk, 1998) and likely caused a large increase in sedimentation rates together with large-scale illegal logging practices (Anon, 2000) with disrupting consequences for the aquatic ecosystem (e.g. Mackinnon et al., 1997). In Indonesia one representative freshwater dolphin population occurs in the Mahakam River in East Kalimantan, i.e., the facultative river dolphin Orcaella brevirostris, commonly and locally referred to as Irrawaddy dolphin and pesut, respectively. The species is found in shallow, coastal waters of the tropical and subtropical Indo-Pacific but also in three major river systems: the Mahakam in Indonesia, the Ayeyarwady in Myanmar, and the Mekong crossing through Vietnam, Cambodia and Laos (Stacey & Arnold, 1999). These river populations were all identified to consist of less than 100 individuals based on preliminary studies and faced ongoing and pervasive threats to their long-term persistence (Kreb, 2002; Smith et al., 2003). In order to identify and monitor the population status and threats more thoroughly and set a rationale for conservation action, a 3.5-years study from February 1999 until August 2002 was initiated. This article presents the results of this study and an in-depth analysis of habitat preferences, population dynamics, threats and recommendations for future conservation activities of the Irrawaddy dolphin population in the Mahakam River. Since 1990 the species has been fully protected by law in Indonesia and is adopted as a symbol of East Kalimantan Province. Prior to the present study, no systematic data had been collected before on the Mahakam population. A two-month preliminary study in 1997 revealed that sighting rates (0.06 dolphins/ km) in the middle Mahakam river segment (with highest dolphin densities) were very low (Kreb, 1999). Based on data we collected during 1999 and 2000, the IUCN status of this freshwater population was raised from ‘Insufficiently Known’ to ‘Critically Endangered’ (IUCN, 2003)
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Study area
The Mahakam River is one of the major river systems of Borneo and runs from 118º east to 113º west and between 1º north and 1º south (Fig 1). Regional climate is characterised by two seasons, i.e. dry (from July-October, southeast monsoon) and wet (November-June, northwest monsoon) (MacKinnon et al., 1997). The river measures about 800 km from its origin in the Müller Mountains to the river mouth. Rapids start upstream of Long Bagun at c. 600 km from the mouth, which limit the dolphins from ranging further upstream. Three major lakes and nearly all major tributaries and many smaller swamp lakes are connected to the main river system in the Middle Mahakam Area (MMA) between 180 km until 375 km from the mouth. These lakes are very important fish-spawning grounds and replenish the main river seasonally. Therefore, the MMA is an area of intensive fishing activity with an annual catch of 25.000 to 35.000 metric tons since 1970 (MacKinnon et al., 1997). Coal mining and logging companies occur along the entire length of the Mahakam River, especially in the tributaries. A large gold digging company is located in the upper Mahakam River segment together with several small-scale, illegal gold mines. Infrastructure is poorly developed in East Kalimantan and the Mahakam River is the main transport system.
METHODS
Field methods
We searched the Mahakam River from the delta to upper rapid streams (600 km from the mouth) by boat from February 1999 until August 2002 for a total of 8925 km (837 hours), and observed river dolphins for a total of 549 h. We conducted 12 involved extensive monitoring surveys in 6 survey periods, which covered the entire distribution range (average duration 10 days; SD ± 2 days) during all types of water levels (high, low, medium, increasing, decreasing) to invest distribution patterns, annual recruitment and estimate population abundance using strip-transects, direct counts and mark-recapture techniques through photo-identification, which are more described in detail in Kreb (2002 & in press a). The distribution range was divided in 15 strip- transects (main river and tributaries) and 2 line-transects (Melintang and Semayang Lakes). Each transect could be finished in one day. Another six intensive surveys (average duration 12 days; SD ± 3 days) were conducted in areas of high dolphin density to investigate preferred habitat and to locate dolphin groups for further focal group follows (see below) to assess daily home ranges (Figure 1). To monitor abundance and locate groups, surveys were conducted with 12-16 m long motorised vessels (12-21 hp), travelling at an average speed of 10 km/ h.
84 Conservation of riverine Irrawaddy dolphins in Borneo
Conservation of riverine Irrawaddy dolphins in Borneo Kedang Rantau Muara Kaman Loa Kulu Kota Bangun Kedang Kepala
Batuq 85
Semayang
Jempang Melintang Tepian Ulak bution area, b) areas of high dolphin density and c) coastal Irrawaddy dolphin area. Muara Pahu Muara Muara Jelau Bohoq Muyub Ulu Rambayan Kedang Pahu Damai
Muara Benangak Datah Bilang Long Bagun Figure 1. Study area with a) total dolphin distri
85 Chapter 6
The photographic effort during the extensive monitoring surveys was one hour per sighting with a total observation effort of 545 h. Durin observation team existed of three active observers: two front observers and one rear observer. The average observation time and g all surveys 2074 photographs were made of dorsal fins. For each sighting, the duration, location, group behaviour, group size, group composition and environmental data, i.e. depth, clarity, surface flow rate, temperature, pH and type of river section (river bend, straight stretch or confluence area) were collected. On average five times a day, similar random samples were collected as those obtained during sightings, whereas type of river section was recorded every fifteen min. In order to assess daily home ranges, 58 groups were followed for 321 h in total and on average 5.5 h daily (range 1.5-13 h) using a motorized canoe of 5 hp outboard engine maintaining an average distance of 50 m. In addition, land-based observations were made in the confluence area of Muara Pahu, c. 300 km upstream, which was frequented daily by different dolphin groups. On average, five sequential days (32 days in total) of land-based observation have been completed by two observers, which overlooked the area some 7 until 10 meter above the water surface (depending on water levels) during six different survey periods for a total of 286 h. When a group of dolphins was sighted, we recorded group size and composition (Kreb, in press a), changes in group-composition, and time spent in the area. Formal interviews were conducted using questionnaires with mainly open questions with residents and fishermen (n = 258) in six important dolphin areas to determine their knowledge and attitude with regards to the dolphins and their conservation. Respondents were questioned separately to ensure independence of data. In order to assess the minimum annual birth rates between November 2000 and November 2001, the total number of different newborns were counted during 5 different surveys (both extensive and intensive surveys), which were more or less equally distributed over the year with an average 2.5-month gap in between the surveys. Newborns encountered during each of these surveys were assumed different than those encountered during an earlier survey. We defined newborns to be of less than one month of age if they complied with all three categories: 1) exhibited an awkward manner of swimming and surfacing, 2) spent all their time in close proximity to an adult and 3) were of less than ½ the average length of an adult, following Bearzi et al. (1997). Mortality was estimated from own observations and semi-structured interviews conducted during a preliminary survey in 1997 and during the surveys from February 1999 until August 2002. Mortality was traced back as far as 1995. Incomplete or untrustworthy accounts with missing locality, date, and traceable eyewitnesses were disregarded (14% of n = 44). Dolphin reactions towards different types of boat traffic were tested by comparing dolphin group surfacing frequencies in presence and absence of different types of boats (see Kreb & Rahadi, in press b, for a more detailed method description)
86 Conservation of riverine Irrawaddy dolphins in Borneo
Analysis
To assess the importance of different river areas in terms of dolphin densities, the river was divided in seven areas where at least one dolphin sighting was made. Total sightings made in each of these different areas during 10 extensive surveys were compared using a chi-square test. Sightings in tributaries within 1 km of the confluence area were considered main river sightings. Sighting rates, densities and abundance estimates based on strip-transects and direct counts were calculated according to the formula described in Kreb (2002). Since no sightings were made in any of the lakes during these extensive surveys, no analysis of the conducted line- transects was required. The mean abundance estimates and coefficient of variation (CVs) of two replicated surveys within each survey period, were added for all survey periods and averaged to obtain the total mean population size (and mean CV). In addition, abundance estimates were calculated per water level condition (combining different years) averaging the estimates of each replicated survey. This was done since there was no trend in abundance (see Results, Trends in abundance), and there was no difference between the variation in abundance estimates per replicated survey within the same time period and the variation in abundance estimates of surveys conducted in different periods but at similar water level conditions. Because all rear sightings (n=9) were associated with the dolphins’ positions in river bends (which is an unpredictable variable), no detection correction factor g(0) was used to calculate abundance and associated CVs. Instead, rear sightings were directly included in the abundance estimates. Also, no seasonal variation was found in sizes of groups (see Results, Population composition) so this component was also not included in the calculation of CVs. Abundance was also estimated using both the Jolly-Seber and Petersen mark- recapture methods based on 728 selected identifiable dorsal fin pictures (Kreb, in press a). Mean population size was calculated as the average of the mean abundance estimates from strip-transects, direct counts and mark-recapture analysis. Mean group size in the Mahakam was based on all on-effort sightings made during nine extensive abundance surveys covering the entire distribution range. Groups were considered different if a group joined after 15 min of observation or groups split during observation time. To detect any trend in abundance, regression analysis was applied to the natural logarithm of 5 mean strip- and direct count abundance estimates over a 2.5 years period (early 1999 until mid 2001). Statistical power was calculated by means of a linear regression program TRENDS (Gerrodette, 1993). The same analysis was performed to detect if there was any trend in mortality using data from 1995 until 2001. Random environmental samples i.e., depth, flow rates, pH, temperature and clarity were compared with samples collected at dolphin locations per water level using a two sample T-test, prior to which a two-tailed F-test was applied to test for similar variances, which were equal for all sample comparisons. Dolphin-preferred areas within the main river were investigated by comparing the percentage of dolphin
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sightings made per water level in straight stretches, river bends and confluences during ten strip-transects surveys that covered the same area using a chi-square test. The relative random availability of straight stretches, river bends and confluences were tested using a chi-square test. When df was 1, Yates correction factor was applied. To identify the year-round significance of a confluence area, for which highest dolphin densities were found, the numbers of identified dolphins per water level were compared using a chi-square test. To prevent biases, the correlation between the number of pictures obtained and number of identified dolphins was tested using the Product Moment Correlation Coefficient. Daily home ranges were estimated by measuring the distance between the two most widely separated sighting locations of the focal group. Minimum annual birth rate was estimated by dividing the total number of newborns encountered in one year (see Methods) with the mean population size. Minimum annual mortality rate was estimated by dividing the number of dead dolphins during the study period (interviews + observations) by years and mean population size.
RESULTS
Abundance and distribution
During ten extensive surveys, we made 76 on effort sightings of Irrawaddy dolphins in the Mahakam (Table 1). The actual dolphin sightings were confined to the area in the main river between Muara Kaman (c. 180 km from the mouth) and Datah Bilang (c. 480 km from the mouth) and the tributaries Belayan, Kedang Rantau, Kedang Kepala, Kedang Pahu, Ratah and Semayang Lake. The cross-shaded area (Figure 1) of 195 km length in the main river from Muara Kaman until Muara Benangak (c. 375 km from the mouth) represents an area of high dolphin densities. The total dolphin distribution area in the Mahakam, based on sightings and interviews with fishermen, starts about 90 km upstream of the mouth at Loa Kulu and ends some 600 km upstream at the rapids past Long Bagun, including several tributaries and two lakes (Figure 1, single- shaded areas). Significant differences were found in sighting density among eight survey areas where we made sightings (X2 = 35.91, df = 7, P < 0.01) (Table 1). The three areas where most sightings were made include several confluence areas with tributaries and lakes. Seasonal variation in distribution pattern is summarized in Table 2 and illustrated in Figure 2. At medium water levels sighting rates in the main river and tributaries are similar. At prolonged high-water levels dolphins were more often found in the main river than in the tributaries, whereas at rising high water levels (data not tabulated since incomplete total area coverage) a lowest mean sighting rate (0.03 dolphins/ km) was recorded in the main river indicating that dolphins had moved upstream into the tributaries. At low water levels no dolphins were sighted in the tributaries.
88 Conservation of riverine Irrawaddy dolphins in Borneo
All but one sighting of Irrawaddy dolphins in and near the Mahakam delta were offshore the delta at low tide (n = 4), whereas one sighting was made 10 km upstream of the delta at high tide. A mean salinity of 21 ppt was measured at dolphin
Table 1 Priority areas for conservation based on the combination of dolphin densities, presence of newborns, observed matings and mortality, with low numbers indicating high priority.
River survey segments of 40 km Priority area Dolphins/ Newborns Mating Deaths length * km < 2 months events ** Muara Kaman – Kota Bangun 2 0.13 12 Kota Bangun – Batuq 3 0.16 1 1 Batuq – Tepian Ulak 5 0.1 1 1 Tepian Ulak – Rambayan – Muara Jelau 1 0.31 8 1 13 Rambayan – Bohoq 6 0.04 2 Bohoq – Muara Muyub Ulu 6 0.04 Ratah 4 0.12 1 Muara Jelau – Damai 6 0.04 1
* Actual proposed conservation areas (1–3) are confined to smaller areas based on frequent sighting locations (see results); ** Dolphins that died between 1995 – 2001 in the survey area; 5 dolphins
died outside the survey areas and 2 dolphins died with unknown location.